1) Marinate the chicken. Mix together the chicken with all the marinade ingredients in a medium bowl and set aside for 30 minutes.
2) Mix together all the sauce ingredients in a medium bowl and set aside.
3) Heat 2 tablespoons oil in a wok over high heat. Sear the chicken, remove from the wok and set aside.
4) Turn the heat to low and add another tablespoon oil. Add the garlic, ginger, chilies, and Sichuan peppercorns. Cook for a minute or two until fragrant.
5) Add the chicken back to the pan along with the spring onions and turn up the heat to high. Stir-fry for a minute, add the sauce to the wok and stir-fry for another minute. The sauce should thicken very quickly.
6) Finally, add the peanuts. Give everything a final stir, sprinkle with spring onion greens and serve.