Place a clean kitchen towel or two paper towels on a plate. Discard the tofu liquid and place the block onto the towel. Fold the towel over the block or place two more paper towels on top of the tofu. Place a heavy item on top of it (not so heavy as to crush the tofu, just heavy enough to release the liquid). Drain the tofu for 30 minutes.
Meanwhile, make the sauce. In a small bowl, mix together the soy sauce, rice vinegar and sugar.
Slice the tofu into 1-inch cubes and place them in a large bowl. Toss the tofu with the cornstarch, until coated.
In a large skillet, heat 2 tablespoons of the sesame oil over high heat. Add the tofu to the pan, working in batches if necessary, cook until lightly browned on all sides, about 15 minutes total. Transfer the tofu to a paper towel lined plate. Repeat with remaining tofu.
Add one tablespoon of sesame oil to the same skillet over medium heat. When the oil is glistening, add the bell peppers and cook, stirring occasionally, until beginning to soften, about 4 minutes. Stir in the green onions, cashews, ginger, garlic, and chili peppers. Cook, stirring, until fragrant, about two minutes longer. Pour the sauce over the vegetables, stir to combine and bring to a simmer. Stir in the tofu and continue to simmer until the sauce has thickened, about 2 minutes.
