Combine the marinade ingredients ahead of time, but marinate the fish for only one hour before grilling. The lime juice will infuse the fish with citrus flavor without softening its texture.

Ingredients
6,  4-ounce  fresh or frozen swordfish or tuna steaks, cut 3/4-inch thick
1/2  teaspoon finely shredded lime peel
1/4  cup lime juice
2  teaspoons cooking oil
2  cloves garlic, minced
1  tablespoon snipped fresh cilantro
1  teaspoon coarsely ground black pepper
1/4  teaspoon salt

Directions
1. Thaw fish, if frozen. For marinade, combine lime peel, lime juice, oil, garlic, cilantro, pepper, and salt. Place fish in a plastic bag set into a shallow dish. Pour marinade over fish in bag. Seal bag; turn to coat well. Refrigerate 1 hour, turning bag occasionally. 

2. Remove fish from marinade; discard marinade. Place fish on greased grill rack directly over medium coals. Grill 6 to 8 minutes or until fish flakes when tested with a fork, turning once halfway through grilling time.  

3. Or, preheat gas grill. Adjust heat for direct cooking. Place fish on greased grill rack over medium heat. Grill uncovered as directed in step 2. Makes 6 servings. 

Source: Better Homes & Garden