In a small bowl, combine all the sauce ingredients and whisk well. Set aside.
In another bowl, combine all the chicken and marinade ingredients except for the cornstarch. Let it marinate for 10 minutes.
After marinating, sprinkle the cornstarch over the chicken, ensuring each piece is fully coated. Shake off any excess.
Heat a wok with about 2 inches of vegetable oil over high heat. Once hot (325°F), fry the chicken until golden and cooked through, about 3-4 minutes per batch. Drain on a paper towel-lined plate.
Discard the oil from the wok and wipe it clean. Heat 1 tablespoon of vegetable oil over high heat. Sauté the onion for 1 minute, then add the bell peppers, dried red chilies, garlic, ginger, and Sichuan peppercorns, cooking for another 1-2 minutes.
Add the cooked chicken back to the wok and pour the sauce mixture over everything. Toss well and stir fry for an additional minute. Serve immediately.