Firstly, cut the tofu into 1 cm thick slices. You can either cut 2-3 pieces of tofu for each burger, or one large slice.
In a medium bowl, mix together the cornstarch, salt, and chilli powder. Set aside.
Add the sunflower oil to a frying pan over medium heat. Once the pan is hot, coat the tofu thoroughly in the cornstarch mixture, before adding to the frying pan.
Cook the tofu for 3-4 minutes on each side until golden and crisp.
Prepare the sticky sauce by mixing together the soy sauce, sweet chilli sauce and rice vinegar in a small bowl.
Layer up the bread rolls with the sauce, rainbow vegetables, and the crispy tofu. Serve immediately.