1Prepare the relish first and set it aside while you prepare the fish. Combine all relish ingredients in a small bowl and stir occasionally.
Prepare the grill. Rinse fish; pat dry with paper towels. Combine lemon juice, butter and garlic in a bowl; mix well. Coat both sides of filets lightly with some of the butter mixture; sprinkle with lemon pepper.
2Place fish in a greased grill basket, tucking under any thin edges. Or, grill fish directly on the greased rack of the grill.
3For a charcoal grill, place grill basket or fish on the rack of an uncovered grill 4 to 6 inches above a solid bed of hot coals (you can hold your hand at grill level only 2 to 3 seconds) and grill until fish is barely opaque and flakes easily when tested with a fork (allow 4 to 6 minutes per 1/2-inch thickness of fish), turning basket once halfway through grilling, basting with remaining butter mixture.
4For a gas grill, preheat grill on high for 10 to 15 minutes. Reduce heat to medium. Place grill basket on grill rack over heat. Cover and grill as above.