Fill a medium pot with water and set it over high heat. Bring the water to a boil so the potatoes can cook first.

Add the potato cubes to the boiling water in the pot. Cook them for 6 to 8 minutes, until they are just tender when pierced with a knife but not falling apart.

Drain the potatoes in a colander. Let them sit for a minute so extra water can steam off.

While the potatoes cook, pat the tofu dry with paper towels if it still feels damp. Keep the cubes fairly even so they brown at the same rate.

Set a large nonstick skillet over medium-high heat. Add 2 tablespoons of the oil and let it heat for about 30 seconds.

Put the tofu cubes into the skillet in a single layer. Cook them without moving them for 4 minutes, until the bottoms look golden.

Turn the tofu in the skillet and cook for 4 to 5 minutes more, turning once or twice, until several sides are browned. Transfer the tofu to a plate.

Lower the heat under the skillet to medium. Add the remaining 1 tablespoon oil.

Add the mustard seeds to the skillet. Cook for 20 to 30 seconds, until they sizzle and a few begin to pop.

Add the sliced onion to the skillet. Cook for 2 minutes, stirring often, until it starts to soften.

Add the grated ginger and turmeric to the skillet. Stir for 30 seconds, until the onion is evenly coated and the spices smell fragrant.

Add the sliced cabbage and 1 teaspoon of the salt to the skillet. Cook for 3 to 4 minutes, stirring often, until the cabbage wilts down and turns glossy.