Drain tofu and wrap in paper towels or a clean dishcloth. Place weights on top, like a cast iron pan or a stack of books. Wait for about 20 minutes for the water to be released.
Slice tofu into 1/2-inch cubes.
In a zip-log bag, or container with a lid add nutritional yeast flakes, onion, powder, garlic powder, paprika, salt cornstarch. Add tofu cubes, close bag, and shake to coat tofu cubes. If you want tofu with a chewier texture then freeze tofu before preparing it.
Heat oil in a large saucepan over medium-high heat. Add the tofu cubes, and pan-fry until golden brown and crispy, about 4-6 minutes on the sides. You can also bake tofu cubes on a prepared baking sheet at 400 degrees F. for about 25-30 minutes, turning halfway.
Add bell pepper and garlic, and saute, stirring for one minute.
Add sweet and sour sauce, bring to a boil, stir in the cornstarch slurry, and stir until thick and bubbly. Garnish with green onion and serve immediately.