Powell struck in the 69th minute following confusion in the Spurs penalty area and the England left-back scored against the team he supported as a boy.
The boss feels that the game was 'given away' by a mistake after a period in which Spurs had several chances to take the lead.
"It goes without saying how disappointed I am," said Glenn afterwards. "Moreso about the way we've given the game away rather than what happened out there.
"We've handed it to them on a plate really.
"Ledley's made a mistake, he's got to see danger and he's got to clear it - that's something he's got to learn from.
"I was particularly disappointed after the best spell of the game for us, for 20 minutes, Gus misses two golden chances for us and then we give a stupid goal away. It sums our season up really."
Glenn Hoddle confessed his disappointment after a second half Chris Powell goal handed Charlton a 1-0 win at the Lane.