Before kick-off Lennon confirmed that Hooper had turned down a contract offer while also revealing that the club had rejected another offer from Norwich after rebuffing a bid, reported to be about £5million, for the 24-year-old last week.
Hooper, who has 18 months left on his current deal, showed why he is attracting increasing interest when he converted a Georgios Samaras pass in the 19th minute before midfielder Victor Wanyama headed in number two before the break.
Former Scunthorpe striker Hooper struck again 10 minutes from time to take his tally to 22 before he set up substitute Scott Brown for the fourth as United, whose boss Peter Houston will leave at the end of the season, were left thankful that their defeat had not been more demoralising.
Lennon tinkered with his side following their 4-1 home win over Hearts. Defender Thomas Rogne, midfielder Beram Kayal and striker Lassad Nouioui came in for Adam Matthews, Brown and Kris Commons, the latter out of the squad altogether with a rib injury. United were unchanged from their fine 3-2 win against Kilmarnock at Rugby Park on Saturday.
Celtic were captained by Samaras and in the third minute he headed a Charlie Mulgrew free-kick past the post from eight yards.
However, a minute later United winger Gary Mackay-Steven missed a great chance to open the scoring after a one-two with Johnny Russell left him through against Lukasz Zaluska. With the Hoops defence missing, the United winger had time and space but his shot slipped past the far post.
It was Celtic who were first to benefit from poor defending at either end when Lassad raced away on a counter-attack with the United rearguard chasing, and when he moved the ball wide to Samaras his first-time pass to the unmarked Hooper saw him confidently beating United keeper Radoslaw Cierzniak.
Celtic doubled their lead in the 33rd minute when Mulgrew's corner was cleared out to Mikael Lustig. He swung a cross to the back post for the unmarked Wanyama to power a header back across goal and into the net.
Celtic started the second half with Lassad heading Joe Ledley's cross over from six yards and there was little to suggest United could stage a comeback.
In the 69th minute Samaras got on the end of Emilio Izaguirre's cross from the left but Cierzniak saved before the visitors survived another spell of activity around their box.
However, 10 minutes from time Celtic broke with pace again and Samaras set up Hooper to score with a neat flick at the near post.
Anthony Stokes replaced Lassad to make his first appearance since last August after recovering from an ankle injury, but it was Brown, on for Kayal, who curled in goal number four after taking a Hooper pass, to leave the champions 12 points clear of Inverness at the top of the table.