Grilled Tuna Steaks with Lemon and Capers

1. Rinse tuna steaks and pat dry with paper towels. Arrange steaks in a shallow glass baking dish. In a small bowl, combine lemon juice, lemon zest, shallots, capers, and parsley. Pour over fish, turning tuna to coat. Marinate at room temperature for 15 minutes or covered in the refrigerator for 1 hour.
2. Prepare a ridged cast-iron stove top grill or outdoor grill. Season the tuna with salt (if using) and pepper to taste. For medium-rare, grill tuna about 3 minutes per side, turning once, until flesh begins to pull apart. For medium cook 2 minutes more until the flesh flakes when prodded with a fork. Remove to a cutting board to rest.
3. Meanwhile in a small saucepan, bring the marinade to a rapid boil. Arrange the tuna steaks on warmed dinner plates and spoon 1 tablespoon of the marinade over each steak. Serve at once.