Combine all of the ingredients in a large, nonreactive bowl (glass, stainless steel, or glazed ceramic), and mix gently with a spoon. Set aside. You can prepare this salsa up to a few hours before serving and store it in the refrigerator in a covered container.
In a deep, nonreactive dish (glass, stainless steel, or glazed ceramic), marinate the fish with the other ingredients for 20-30 minutes before grilling.
Grill over coals or on a grill, or cook under a broiler for 6-8 minutes per side.