Prepare an outdoor grill. At least 30 minutes in advance, combine the salsa ingredients in a nonreactive bowl. (The salsa may be made and refrigerated up to 2 days in advance.)
Coat the fish with the olive oil and season with the salt and pepper. Grill the fillets about 7 to 8 inches from the heat source for 1 1/2 minutes. Rotate the fillets 45° to make an attractive crosshatch pattern and cook 1 1/2 minutes more. Turn and cook for 1 1/2 minutes.
Alternatively, heat a grill pan until very hot, about 3 minutes. Sear the fillets following the time schedule above. The fish is done when it is almost firm. Remove the fillets to plates, crosshatched side up. Stir the salsa, spoon it generously over the fish, and serve.