Put the rice and 1 1/2 cups water in a medium saucepan and set it over high heat. Bring the water to a boil.

Cover the saucepan, turn the heat to low, and cook the rice for 15 minutes. Take the pan off the heat and let it sit, still covered, while you make the stir-fry.

Pat the tofu dry with paper towels. Put the tofu cubes in a medium bowl.

Sprinkle 1 tablespoon of the cornstarch over the tofu in the bowl. Toss gently so the cubes are lightly coated.

Put the soy sauce, rice vinegar, brown sugar, and the remaining 1 tablespoon cornstarch in a small bowl. Add 1/3 cup water and stir until the cornstarch dissolves and the sauce looks smooth.

Set a large skillet or wok over medium-high heat. Add 1 tablespoon of the oil and let it heat for about 30 seconds.

Add the tofu to the hot skillet in one layer. Cook without moving it for 3 to 4 minutes, until the bottoms look golden.

Turn the tofu with tongs or a spatula. Cook for 3 to 4 minutes more, turning as needed, until several sides are browned. Transfer the tofu to a plate.

Add the remaining 2 tablespoons oil to the same skillet. Add the broccoli and red bell pepper.

Stir-fry the vegetables for 2 minutes, until the pepper starts to soften and the broccoli turns bright green in spots.

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

Add 2 tablespoons water to the skillet. Cover with a lid and cook for 2 minutes, until the broccoli is crisp-tender, which means cooked through but still a little firm.