Prepare the tofu: Place the tofu in a large bowl and gently toss with the cornstarch, ensuring each piece is generously coated. Add more cornstarch if needed.
Air-fry the tofu: Spray the inner basket of the air fryer with oil. Arrange the tofu cubes in a single layer in the basket and spray the tops with more oil. Air-fry at 390°F (200°C) for about 15 minutes, shaking the basket halfway through, until the tofu is golden brown and crispy.
Make the spice mix: In a small bowl, combine the white pepper, black pepper, salt, and Sichuan peppercorns (if using). Set aside.
Cook the aromatics: While the tofu is air-frying, heat the oil in a large nonstick pan or skillet over medium-low heat. Sauté the garlic, chile, and white parts of the scallion for about 45 seconds, until fragrant and the garlic starts to turn golden.
Once the tofu is done, add it to the pan with the aromatics. Stir to coat the tofu evenly. Sprinkle half of the spice mix over the tofu and quickly toss to combine, ensuring an even coating. Taste and add more of the spice mix if needed.
Finish and serve: Garnish the tofu with the green parts of the scallion and serve immediately.