For tabletop grill:
Preheat grill according to manufacturers directions. Place tomato halves on grill rack. If using a covered grill, close lid. Grill until tomatoes are very tender. For covered grill, allow 3 to 4 minutes. (For open grill, allow 6 to 8 minutes, turning tomatoes once halfway through grilling.) Remove tomatoes from grill; set aside. Add fish fillets to grill, tucking under any thin edges if using whole fillets. If using a covered grill, close lid. Grill until fish flakes easily when tested with a fork. For covered grill, allow 2 to 3 minutes. (For open grill, allow 4 to 6 minutes, turning stacked fillets or halved fillets once halfway through grilling.) Continue as directed in Step 4 above.
*Test kitchen Tip:
If grill pan is large enough, tomatoes and fish may be grilled at the same time.