Place the tofu in a large bowl with the cornstarch, salt, and pepper. Toss to combine until the tofu is thoroughly coated.
Heat 2 tablespoons of oil in large sauté pan over medium-high heat.
Once the oil is hot, add the tofu to the pan and cook, tossing occasionally, until all sides are golden and crispy, 10 to 15 minutes. Using a slotted spoon, transfer the tofu to a paper-lined plate.
Meanwhile, make the sauce. Whisk all its ingredients in a bowl. Taste and adjust seasonings, if necessary and set aside.
In the same pan you sautéed the tofu in, add 1 tablespoon of oil over medium-high heat.
Once the oil is hot, add the onions and chilis, and stir fry until the onions are slightly translucent, 2 to 3 minutes.
Toss in the green beans and bell peppers and continue to cook, stirring often, until they become crisp-tender, 5 to 7 minutes.
Add the garlic and green onion, and cook for another 1 to 2 minutes, until fragrant.
Pour in the sauce, mix to combine, and simmer until the sauce thickens, 3 to 5 minutes.
Stir in the reserved tofu, mixing to coat.
Serve immediately and garnish with minced green onion and crushed peanuts over white rice. Enjoy!