Heat oil in wok or 10-inch skillet until hot. Stir-fry garlic until light brown. Add pork; stir-fry until brown, 6 to 8 minutes. Spoon off fat. Add peppers, sugar and fish sauce; stir-fry 2 minutes. Add peanuts and 2 tablespoons cilantro; stir-fry 1 minute. Spoon pork mixture onto pineapple slices. Sprinkle with cilantro.