Set a large nonstick skillet and a plate by the stove so they are ready when you start cooking.

Drain the tofu. Wrap it in paper towels or a clean kitchen towel, put it on the plate, and set something heavy on top, such as the skillet or a few cans, for 5 minutes to press out extra water.

Unwrap the tofu and cut it into 1-inch cubes.

Put the tofu cubes and the cornstarch in a medium bowl. Toss gently until the tofu is lightly coated on all sides.

In a small bowl, stir together the hoisin sauce, soy sauce, rice vinegar, and water until smooth.

If you have not done it yet, thinly slice the red bell pepper and yellow bell pepper, trim the snap peas if needed, and keep the sliced scallion whites separate from the greens.

Place the skillet over medium-high heat. Add 2 tablespoons of the oil and heat it until it looks shiny.

Add the tofu to the skillet in a single layer. Leave it alone for 3 to 4 minutes so the first side can brown.

Turn the tofu pieces with a spatula. Cook for 4 to 5 minutes more, turning once or twice, until several sides are golden brown and the tofu feels firmer.

Transfer the browned tofu from the skillet to the plate.

Add the remaining 1 tablespoon oil to the same skillet.

Add the scallion whites to the skillet. Stir for about 30 seconds, just until they smell fragrant.