Preheat oven to 425 degrees F (220 degrees C). Line a shallow roasting pan with aluminum foil.
Place pork in roasting pan. Combine 3 tablespoons brown sugar, mustard, and ginger in bowl; spread over pork.
Bake in preheated oven until juices run clear and a meat thermometer reads 160 degrees F (71 degrees C), about 35 to 40 minutes. Let stand 10 minutes before slicing.
Combine pineapple, peppers, green onions, cilantro, and 1 tablespoon brown sugar in a bowl. Serve with pork.