- Place fish in a non-aluminum dish large enough to hold it in a single layer.
- Combine tequila, triple sec, lime juice, salt, garlic, and 2 tsp oil and pour over the fish, rubbing all over.
- Cover and marinate for ½ hour at room temperature or up to 3 hours in the refrigerator, turning occasionally.
- Just before serving, combine tomatoes, onions, chilies, cilantro, sugar and salt to taste.
- Heat the grill to very hot.
- Remove fish from marinade, pat dry (reserving marinade) and brush lightly with 1 t oil and grind pepper over the surface.
- Cook on a greased grill for about 4 minutes per side, or until flesh is opaque.
- Meanwhile, boil marinade in a saucepan for 2 minutes, remove and discard garlic cloves, and spoon a little over the fish.
- Spoon tomato salsa alongside and serve.