Cut half a block of firm tofu into bite size blocks. Stirfry it in a wok or frying pan with some nonstick cooking spray until slightly browned/cooked.
Take the tofu out of the pan. Add to the empty pan - half a chopped white onion, two handfuls of chopped red and green bell peppers, and some canned diced or cut pineapples with juice. Cook over medium high heat and simmer until juices are reduced.
Add the tofu back into the pan, plus some sweet and sour sauce. [I used approx 4-5 oz]
Serve with hot rice.