Coat the tofu in cornflour and then fry in hot oil until golden.
Stir fry the peppers in a splash of oil for a few minutes.
Add the spring onions, broccoli, pineapple, ketchup, vinegar, sugar and stock. Give it a good mix and bring it up to a boil.
Mix the remaining 1 tbsp of cornflour with a splash of water until you have a thick, but still slightly runny paste - stir it into the sweet and sour tofu sauce. Then add tofu.