In a medium bowl, mix peanut butter, green onions, soy sauce, lemon juice, brown sugar, garlic, coriander, and cayenne pepper; add pork, and stir to coat. Cover, and marinate in the refrigerator at least 30 minutes.
Preheat grill for high heat. Thread marinated pork, water chestnuts, green bell pepper, red bell pepper, and sweet onion alternately onto skewers. Transfer remaining marinade to a small saucepan, bring to a boil, and cook for several minutes.
Lightly oil grate. Cook skewers for 10 minutes, or to desired doneness. Turn skewers while grilling to cook evenly, and brush with boiled marinade during last few minutes.
