Cut the pressed tofu into bite-sized cubes and set aside.
In a large bowl, combine cornstarch, salt, black pepper, garlic powder, onion powder, and cayenne pepper (if using). Mix well.
Add the tofu cubes to the bowl and gently toss until all pieces are evenly coated with the cornstarch mixture.
Heat the vegetable oil in a large skillet over medium-high heat. Once hot, carefully add the tofu cubes in a single layer, ensuring not to overcrowd the pan. You may need to do this in batches.
Fry the tofu for about 3-4 minutes on each side, or until golden brown and crispy. Use a slotted spoon to remove the tofu and place it on a paper towel-lined plate to drain excess oil.
Serve the crispy tofu hot, garnished with sliced green onions and lemon wedges on the side.