Place cubed tofu in a bowl with cornstarch and toss to evenly coat.
Heat sesame oil in a large pan over medium-high heat, then fry tofu in a single layer for 2-3 minutes per side or until golden brown. Remove cooked tofu and set aside.
Add garlic, ginger, and white parts of scallions to pan and cook for 2-3 minutes or until fragrant.
Add in red and green bell peppers, sauté for 2-3 minutes then place tofu back into pan along with green parts of scallions and cashews or peanuts.
Whisk together all sauce ingredients in a bowl, then pour into pan and reduce heat to a simmer. Simmer until sauce has thickened then serve over rice.