In a large bowl, combine the Szechwan peppercorns, chili oil, ginger, garlic, soy sauce, sake and brown sugar. Mix to blend, then add chicken pieces and stir to coat. Cover and refrigerate for 2 to 3 hours to marinate.

Fill a wok about halfway full of oil for deep-frying. Heat to 365 degrees F (185 degrees C). Reserving marinade, fry chicken a few pieces at a time in the hot oil until golden, 5 to 6 minutes. Remove chicken and set on paper towels to drain.

Clean out the wok and add reserved marinade. Stir in the chicken broth and bring to a boil. Return chicken pieces to the wok, cover and simmer for about 35 minutes, turning the chicken at least once.

Remove the chicken and allow to sit for 10 minutes. Cut chicken into 1 inch pieces and arrange on a platter lined with lettuce leaves. Spoon sauce over the chicken and garnish with green onion.