Heat grill to medium-high. Grill pineapple until you begin to see char marks; not falling apart or mushy. Let cool, dice and mix with the vinegar, olive oil and remainder of the vegetables and seasonings. Cover and refrigerate the pineapple salsa to let marinate for 3 to 5 hours.
PREPARE THE LEMON BUTTER:
Melt the butter and mix with the lemon juice and garlic. Set aside while you grill the fish.
GRILL THE FISH:
Salt and pepper the fish. Grill over medium heat until done. Top with salsa and drizzle with lemon butter.