Heat the oil in a large frying pan over med-high heat. Add the tofu, half the scallions, half the garlic, and the ginger and stir-fry for 3 min. Add the chiles and stir-fry for 1 min. Stir in the sherry, soy sauce, 1 cup water, and salt. Bring to a boil and simmer for 3 min. Mix the remaining 1 Tbsp of water and cornstarch in a small bowl. Stir into the pan and cook until the mixture thickens, 2-3 min. Sprinkle with the remaining scallions and garlic. Transfer to a heated plate and serve hot.