Press the tofu for 20 minutes before you start. It's ideal if you use a tofu press but if you don't have a tofu press then stand the tofu on a plate, with another plate on top of it, and then stack something heavy on top of that like a heavy pot or some heavy books.
Add the soy sauce, garlic powder, onion powder, ground ginger, maple syrup, rice vinegar, sesame oil and hoisin sauce to a bowl or measuring jug and whisk into a sauce (leave the cornstarch until later).
When the tofu has finished pressing, cut it into cubes and place into a glass dish. Pour over the marinade sauce and turn over the cubes of tofu so that both sides are covered in marinade sauce. Place into the fridge and leave to marinate for 30 minutes.
After 30 minutes, heat a frying pan with a little sesame oil. Take the tofu out of the marinade sauce and fry it until golden brown.
Add the teaspoon of cornstarch to the leftover marinade sauce and then pour it over the fried tofu and fry until thickened.