Press the tofu briefly or for up to 30 minutes by wrapping it in a clean towel and pressing firmly with your hands on either side or by placing a weight (e.g. a cast iron pan) on it for up to 30 minutes.
Chop the tofu into one-inch cubes.
Add one tablespoon of the oil to a large skillet or large non-stick frying pan and heat on medium-high heat. When hot add the tofu and fry 2-3 minutes on each side until the tofu is browned and crispy (see notes for air frying or baking instructions)
Chop the onion and peppers.
Rremove the tofu from the pan and add the remaining half tablespoon of oil, increasing heat to high. Add the chopped vegetables when the oil is very hot and stir fry for three minutes until softened.
Whisk together all the sauce ingredients except the cornstarch, and add to the pan along with the fried tofu. Mix to combine. When boiling, reduce the heat slightly and leave to cook for five minutes.
Whisk the cornstarch with two tablespoons of water to make a slurry and add to the pan. Quickly stir to distribute the cornstarch and increase the heat to high. When the mixture is at a lively simmer, reduce the heat slightly and cook for three minutes, stirring often to prevent sticking.
Done! Taste and adjust salt if needed, and increase the chili garlic sauce if you want it spicier.