Put the potato pieces in a large skillet and cover with water. Bring to a boil, then reduce the heat to medium and simmer 3 minutes. Pour out all but about 1 tablespoon of the water.
Add the olive oil, scallions, garlic and chili powder to the skillet and cook, stirring, 2 minutes. Add the bell peppers and 1/2 teaspoon salt and cook, stirring occasionally, until the potatoes and peppers are tender, 5 to 7 more minutes. Add the tofu and 2 tablespoons water and cook until the tofu is heated through, about 3 more minutes. Season with salt.
Warm the tortillas in a skillet or in the microwave. Divide among plates and top with the tofu scramble. Pile the cheese, cherry tomatoes and lettuce on top.