Heat a small, dry saucepan. When the saucepan is hot, add the Szechuan peppercorns and, shaking the pan constantly, toast until the peppercorns are fragrant. Remove from the heat. Place the peppercorns in a spice grinder and grind. Season the chicken pieces with the peppercorns and salt and set aside. Heat a large wok over high heat. When the wok is hot, add the oil. Add the ginger, garlic and onions and stir-fry for 1 minute. Add the chicken, broccoli, peppers, shiitake mushrooms, soy sauce, sherry and chile paste. Stir-fry until the chicken is cooked through and the vegetables are cooked, but al dente, about 5 minutes. Add the scallions and stir-fry for 1 more minute.