Cut tofu into long, rectangular blocks. Mix together corn starch, onion powder, garlic powder and salt.
Coat tofu slices in corn flour mixture and pan fry until crispy (I used about 1 tbsp olive oil)
Mix the marinade ingredients - light soy sauce, dark soy sauce, vinegar, maple syrup and sesame oil. Pour over the tofu in the pan and give it a good mix. Take off heat immediately afterwards.
You can mix in some toasted sesame seeds if you're using the tofu for another dish.
Layer the sandwich with bread, lettuce, tomatoes, carrots, tofu, toasted sesame seeds and vegan mayo in that order.
Cut the sandwich into half and it's ready to eat!