Set a large nonstick skillet or well-seasoned cast-iron skillet over medium heat. Keep a lid or a sheet pan nearby so you can cover the skillet later.

In a small bowl, stir together the soy sauce, rice vinegar, chili-garlic sauce, 1 tablespoon of the cornstarch, and 1/4 cup water until smooth. Set the sauce bowl near the stove.

Put the tofu cubes in a medium bowl. Sprinkle the remaining 1 tablespoon cornstarch over the tofu and toss gently until the cubes have a light, even coating.

Add 2 tablespoons of the oil to the warm skillet and swirl to coat the bottom. Add the tofu in one layer.

Cook the tofu for 4 to 5 minutes without stirring much, until the bottoms are golden brown and release easily from the skillet.

Turn the tofu cubes with tongs or a thin spatula. Cook for 3 to 4 minutes more, until several sides are browned.

Transfer the browned tofu from the skillet to a plate. Keep the skillet on the stove.

Add the remaining 1 tablespoon oil to the skillet. Add the sliced potatoes and 1/3 cup water to the skillet and spread the potatoes into an even layer.

Cover the skillet and cook the potatoes for 5 minutes, adjusting the heat as needed so the water simmers gently instead of boiling hard.

Remove the lid. Cook the potatoes for 3 minutes, stirring once or twice, until the water has cooked off and the cut sides start to turn light golden.

Add the green beans and red bell pepper to the skillet. Cook over medium-high heat for 3 to 4 minutes, stirring often, until the beans are bright green and the pepper is just starting to soften.

Add the scallion whites, garlic, and ginger to the skillet. Stir for 30 seconds, just until fragrant, so the garlic does not burn.