Add the chicken and all the marinade ingredients into a medium bowl. Mix until the marinade coats the chicken evenly. Marinate the chicken while preparing the other ingredients.
Mix the sauce ingredients together in a small bowl until the cornstarch is dissolved.
When you’re ready to cook, slowly add the ¼ cup cornstarch to the marinated chicken while mixing, until the pieces are coated.
Heat the oil in a large pan over high heat until shimmering. Spread the chicken in an even layer. Fry without touching for 2 minutes so that the bottom of the chicken turns golden. Flip to cook the other side until golden and the chicken has cooked through, 2 minutes. Turn off the heat and transfer the chicken to a plate. Give the chicken 2 to 3 minutes to cool off.
Your pan should still have about 1 tablespoon of the oil in it. Add more oil if needed. Add the scallion, dried chili pepper, garlic, ginger, and Sichuan peppercorns. Turn to medium-high heat. Toss until fragrant, 30 seconds or so.
Add the red pepper. Stir and cook for 1 minute, or until just starting to turn tender.
Mix the sauce again so the cornstarch is fully dissolved, then pour it into the pan. Stir a few times until the sauce thickens. Add back the chicken. Stir to coat the chicken evenly. Transfer everything to a plate and serve hot with steamed rice as a main dish.
