Place the diced chicken in a bowl. Mix together all the ingredients for the marinade and pour into the bowl. Mix well. Allow to sit in the fridge for about 30 minutes.
Heat the cooking oil in a wok. When smoking, add the Sichuan peppercorns and chilis. Stir fry until fragrant.
Add the marinated chicken, moving the pieces around to separate them (depending on the size of your wok, you may have to do this in batches). Cook just until the chicken turns a light brown. Scoop everything out — chicken, chilis and peppercorns — and transfer to a strainer.
Pour off the oil, leaving only about three tablespoonfuls. Reheat until smoking.
Add the garlic and ginger; stir fry for a few seconds.
Add the peanuts (and carrot and bell pepper, if using) and stir fry until it smells roasted.
In a bowl, mix together the soy sauce, rice wine, chicken broth, sugar, rice vinegar and starch. Pour into the wok, stirring fast until thick and no longer cloudy.
Return the chicken, chilis and Sichuan peppercorns to the wok. Toss and stir to coat each piece of chicken with sauce. Turn off the heat. Transfer the cooked kung pao chicken to a platter, garnish with chopped greens and serve at once.