FA Cup - Tottenham 3 Southend 1
Robbie Keane had scored the opening goal before Lennon set up Jermaine Jenas for the second with a splendid run from the left of midfield.
Freddy Eastwood's penalty dragged the Championship's bottom-placed club back into the tie, but Lennon then created a goal, this time from the right, for Mido to score.
Although Stewart Downing has played himself into form for Middlesbrough, Lennon could offer a solution to England's problem on the left when England play next month.
Lennon's next task, however, will be to continue his impressive form when Spurs face Arsenal in the Carling Cup semi-final second leg on Wednesday as Martin Jol's men look to extend their unbeaten run of 13 cup-ties.
Southend never looked like ending Spurs' fine run in the cup competitions, despite Eastwood's penalty giving them hope.
They also missed a chance to score immediately after Spurs' first two goals - both misses were by former Tottenham players - and their season will now be focused on survival.
Jenas was making a return from nearly two months out with an ankle injury and he slipped straight back into the pace of the game despite his spell on the sidelines.
He went on a mazy run early on which nearly set up Keane, only for Steven Hammell to get back just in time.
It was Jenas' central-midfield partner, however, who set up the opener in the 12th minute.
Didier Zokora carried the ball from defence to attack over 40 yards before finding Keane on the edge of the area and his shot took a wicked deflection off Hammell to wrong-foot Darryl Flahavan.
Southend, who had lost only one of their last seven matches, immediately missed a glorious chance to restore parity.
Mark Gower, a former Spurs player, was found at the far post by Eastwood's cross, but the midfielder could not get purchase on his volley and Radek Cerny claimed the ball easily.
Cerny, the Czech Republic goalkeeper standing in while Paul Robinson rested, was then reduced to a role of a spectator for the rest of the first half as Spurs went in search for a second.
They peppered Flahavan's goal from all angles, Zokora starting their moves and finding runners such as Lennon to continue attacks.
Keane had chances to add to his opener before the break, screwing a shot wide after Hossam Ghaly got behind the Southend defence, then seeing Flahavan tip his flicked finish onto the bar.
He also attempted an impish first-time volley when there was plenty of time to spare, but the effort flew over the bar.
Lennon was deployed on the left flank and could have doubled the lead in the 19th minute, but his effort was blocked by Adam Barrett and his rebound flew over the bar.
Flahavan, whose heroics kept Southend in the game when they were at White Hart Lane earlier in the season for their Carling Cup quarter-final, was kept busy throughout.
He had to be down smartly at the feet of Paul Stalteri, who was returning from a hip injury, and the goalkeeper then saved at his near post on the half-hour mark from a Young-Pyo Lee shot.
Even Ricardo Rocha, the Portugal centre-back who was making his Spurs debut following his midweek move from Benfica, had a chance, but he headed across the face of the goal from the corner.
Spurs also had two first-half penalty shouts turned down, the first when the ball struck Jamal Campbell-Ryce and the second when Jenas was hauled down by Barrett.
Jenas doubled the lead in the 49th minute, but it was Lennon's pace that created the chance.
The England winger left Lewis Hunt bemused when he flicked the ball around him, and he then twisted and turned his way beyond Campbell-Ryce, with Jenas scuffing the cross in.
Kevin Maher, another former Spurs player, could have reduced the deficit two minutes later, but Cerny tipped over his powerful effort.
Southend, however, were handed a lifeline when Ghaly handled in the area, with Eastwood scoring the penalty.
Mido restored the two-goal advantage, though, with a finish off the underside of the crossbar in the 75th minute after Lennon had crossed, this time from the right.
Tottenham boss Martin Jol praised the versatility of Aaron Lennon after the England winger helped his side reach the fifth round of the FA Cup at the expense of Southend.
Lennon was dazzling on either flank at White Hart Lane, creating two goals in the 3-1 win and causing constant problems for the Coca-Cola Championship's bottom side.
Jol made a raft of changes ahead of the Carling Cup semi-final second leg on Wednesday against Arsenal, but Lennon was not given a rest and showed how he could solve England's problem on the left of midfield.
'We had many changes, some players give us spark and that was Lennon,' Jol said.
'Lennon was good. The evidence is that he had an assist from the left and the right. He can play on either side.
'He's getting stronger. Against Arsenal, he was the probably the best on the pitch and he was the best again.'
It was Didier Zokora, rather than Lennon, who set up the opener.
Zokora broke from defence in the 12th minute and passed to Robbie Keane, whose effort from the edge of the area took a wicked deflection off Steven Hammell.
'We should have scored more goals in the first half,' claimed Jol.
Jermaine Jenas doubled the lead three minutes after the break, scuffing in after Lennon had outfoxed Lewis Hunt and Jamal Campbell-Ryce on the left.
'I was happy that he was there again, full of energy and chasing people down,' said Jol of Jenas, who returned following almost two months out with an ankle injury.
Freddy Eastwood pulled a goal back from the penalty spot after Hossam Ghaly handled, but Lennon crossed for Mido to seal the victory.
'I can't say that 2-0 is comfortable,' said Jol.
'It made it exciting luckily enough we scored the third one.'
Mido picked up a back problem which will require assessment before the Arsenal game.
Dimitar Berbatov has travelled to Germany to see specialist Hans Muller-Wolfhart about his groin injury, and it could leave Jol with just Jermain Defoe and Keane in attack on Wednesday.
Mido has been linked with a move to Manchester City, but Jol said: 'Mido is important because Berbatov is out. We are a club that keeps our best players.'
Southend boss Steve Tilson believes his defenders will not be the last to be troubled by the pace of Lennon.
'He runs most full-backs ragged, whether it's from our league or the Premiership,' said Tilson.
'He played ever-so well.
'Any full-back knows what Lennon is about. When he's on form, he's a very difficult person to mark.'
After taking Spurs to extra-time in the Carling Cup quarter-final last month, Tilson admitted his side were outclassed this time around.
'We were lucky to go into half-time just one down,' he said. 'Tottenham didn't let us play. They closed us down quicker than in the previous tie.
'Credit to them because they made life very difficult for us. That's why they're earning the money they are earning.'