Put the rice in a medium saucepan with 1 1/2 cups water and a pinch of salt. Set the saucepan over high heat and bring it to a boil.

Cover the saucepan, turn the heat to low, and cook the rice for 15 minutes, until the water is absorbed.

Take the saucepan off the heat and let the rice stand, still covered, while you make the stir-fry.

Cut the tofu into 1-inch cubes. Pat the pieces dry again if they still feel wet so they brown more easily in the skillet.

In a small bowl, stir together the soy sauce, brown sugar, cornstarch, and 1/2 cup water until the cornstarch is fully dissolved.

Set a large skillet over medium-high heat and add 1 tablespoon of the oil.

Put the tofu into the skillet in a single layer. Cook for 4 to 5 minutes, without moving it much, until the bottom side is deep golden.

Turn the tofu pieces and cook for 3 to 4 minutes more, until several sides are browned. Transfer the tofu to a plate.

Add the remaining 1 tablespoon oil to the same skillet. Put the onion into the skillet and cook for 2 minutes, stirring often, until it starts to soften.

Add the grated ginger to the skillet. Stir for about 30 seconds, just until it smells fragrant.

Put the mushrooms into the skillet. Cook for 4 minutes, stirring every minute or so, until they release their moisture and begin to brown around the edges.

Add the napa cabbage and the white parts of the scallions to the skillet. Cook for 2 to 3 minutes, stirring, until the cabbage starts to wilt but still has some body.