Fill a medium pot with water and bring it to a boil over high heat for the udon.

Drain the tofu and pat it dry with paper towels or a clean kitchen towel.

Cut the tofu into 1-inch cubes and set the cubes on a plate.

Trim the snow peas. Slice the shiitake mushrooms. Thinly slice the scallions, keeping the white parts and green parts in separate piles.

Peel and thinly slice the garlic. Grate or very finely chop the ginger.

In a small bowl, whisk together the soy sauce, rice vinegar, brown sugar, toasted sesame oil, 1 teaspoon of the cornstarch, and 1/4 cup water until smooth.

Put the tofu cubes in a medium bowl and sprinkle the remaining 2 teaspoons cornstarch over them. Toss gently so the tofu is lightly coated.

Add the frozen udon to the boiling water in the pot. Cook for about 1 minute, just until the noodles loosen and separate.

Drain the udon in a colander and rinse briefly under warm water so the noodles do not clump together. Set the colander near the stove.

Set a large skillet or wok over medium-high heat. Add 2 tablespoons of the neutral oil and heat it until the oil looks shiny.

Add the tofu to the skillet in a single layer. Cook for 3 to 4 minutes, until the bottom side is golden.

Turn the tofu pieces with a spatula. Cook for 2 to 3 minutes more, until another side is browned.