Thaw fish, if frozen. Rinse fish; pat dry. Place fish in a plastic bag set in a shallow dish. For marinade, mix lemon juice, cilantro or parsley, olive oil, garlic, black pepper, and red pepper. Pour over fish in bag; seal bag. Marinate in the refrigerator for 30 to 60 minutes, turning bag occasionally.

Meanwhile, prepare Tomatillo Salsa. Wrap tortillas tightly in foil.

Drain fish, reserving marinade. Lightly spray a cold grill rack with nonstick coating. Place fish on the rack of the uncovered grill directly over medium coals. Place red sweet pepper quarters beside fish and perpendicular to wire of grill rack. Grill fish for 8 to 12 minutes or just until fish begins to flake easily, turning once and brushing once with reserved marinade halfway through grilling. Discard any remaining marinade. Grill sweet peppers for 8 to 10 minutes or until tender, turning occasionally. Place wrapped tortillas on grill rack during the last 5 minutes of grilling.

Flake fish into large chunks with a fork. Cut sweet peppers into 1/2-inch-wide strips. Immediately fill warm tortillas with fish and sweet pepper strips. Serve with Tomatillo Salsa. Makes 4 servings.

Wearing plastic gloves, rinse 2 fresh serrano peppers. Halve peppers; remove seeds, stems, and veins. Finely chop peppers. Remove husks from 3 fresh tomatillos. Finely chop tomatillos (you should have about 1-1/2 cups). Stir together peppers; tomatillos; 3 green onions, thinly sliced (6 tablespoons); 2 tablespoons finely chopped onion; 1 tablespoon lemon juice; 1 tablespoon snipped fresh cilantro or parsley; 1/4 teaspoon salt, and 1 clove garlic, minced.

Up to 2 hours ahead, prepare Tomatillo Salsa. Cover and chill.