Place cubed tofu in large bowl. Add cornstarch and salt, then toss to coat well. Set aside.
Heat neutral oil in large skillet over medium heat. Once oil is hot and shimmering, add tofu cubes. Cook, flipping and stirring periodically, until crisp and browned on all sides.
While tofu cooks, add all sauce ingredients to medium bowl and whisk thoroughly to combine. Set aside.
Transfer cooked tofu to plate or bowl and set aside. Add red chilis, garlic, and ginger to now-empty skillet and sauté until just fragrant.
Add bell peppers and onion to skillet. Sauté until vegetables are softened, approximately 3 to 4 minutes.
Return tofu to skillet and pour in prepared sauce. Stir well to coat, then let simmer 4 to 5 minutes or until sauce has thickened. Serve immediately with desired garnishes and sides.
Notes
Red Chilies: For a milder dish, don't slice the red chilies! Just cook them as-is. You can remove them before eating for the least amount of heat.