Tofu and Spinach Stir Fry

Name: Tofu and Spinach Stir Fry
Ingredients: 8 ounces firm tofu, drained and cut into ½-inch cubes; 3 tablespoons vegetable oil, divided; 1 (1/8-inch-thick) ginger slice, gently smashed with the side of a knife; 3-4 cloves garlic, thinly sliced; Sliced Thai, serrano, or jalapeno chiles; 1 teaspoon chopped shallot (optional); 1 tablespoon soy sauce; 1 teaspoon oyster sauce or fish sauce (optional); 1½ pounds fresh spinach leaves (about 2 bunches), washed and stem ends trimmed; ½ teaspoon sugar