Firm tofu sizzles on a scorching iron plate with onions, peppers, and a savory sauce. This dramatic, protein-rich dish is a family favorite at Chinese restaurants and can be made vegetarian easily.
Press the firm tofu with paper towels to remove excess moisture, then cut into 1/2-inch thick slabs.
Heat 2 tbsp vegetable oil in a large nonstick or cast-iron skillet over medium-high heat. Add tofu pieces and sear 3-4 minutes per side until golden and crisp. Transfer tofu to a plate.
Add remaining 1 tbsp oil to the pan. Stir-fry sliced onions, green and red bell peppers, and garlic over medium-high heat, keeping the vegetables crisp-tender (about 2-3 minutes).
In a bowl, mix soy sauce, oyster sauce, sugar, sesame oil, cornstarch, and black pepper with 3 tbsp water. Pour this sauce into the pan and stir to coat the vegetables. Cook until thickened, about 1 minute.
Return the tofu to the pan, nestling it among the vegetables. Raise heat for 2 minutes for a final sizzle. Scatter sliced scallions on top and transfer everything to a preheated iron plate or heavy dish for serving.