The Chairboys trailed 2-1 at the break after Ade Azeez and Krystian Pearce struck either side of Jo Kuffour's goal for the home side.
But Cowan-Hall scored with two headers to hand Wycombe the lead for the first time and inflict a third successive defeat on Torquay.
The visitors took the lead in the 26th minute when Kevin Nicholson's cross deceived Wycombe full-back Sam Wood allowing Azeez to shoot into the far corner from 12 yards out.
Wycombe equalised a minute later when Kortney Hause played a hopeful ball over the top and Kuffour outmuscled Pearce before beating Martin Rice.
Torquay reclaimed lead in the 37th minute when Pearce, making his first appearance since he was hospitalised with breathing problems last month, headed in from Lee Mansell's corner.
But Wycombe levelled eight minutes after the break thanks to Cowan-Hall's header from Matt Bloomfield's cross.
And the home side took the lead in the 77th minute when Cowen-Hall headed in from the penalty spot with the help of the far post.