SHRIMP MARINADE: In resealable 1-gallon plastic bag, combine 1/4 cup of lime juice with garlic, red pepper flakes, 1 tablespoon of oil, 1/4 teaspoon salt, and 3 to 4 grinds of black pepper. Add shrimp, seal bag, and massage to coat with marinade. Refrigerate for 1 hour.

VEGETABLE MARINADE: Meanwhile, cut frying and bell peppers vertically into thin strips. Cut onion crosswise into 1/4-inch slices. Place vegetables in another plastic bag. Add remaining lime juice and oil, plus 1/4 teaspoon salt and a few grinds of pepper. Seal bag and massage to coat vegetables.

FAJITAS: Seal tortillas in foil, making two packages.

Heat charcoal or gas grill to medium-high heat. Brush grill rack with oil. Or heat grill pan over high heat until a drop of water flicked into it dances.

Drain and pat dry vegetables, discarding vegetable marinade. Arrange them on grill at right angles to bars or pan ridges. When vegetables are well marked, about 2 minutes, remove onions to platter and turn peppers. When peppers are crisp-tender, 1 minute, add to onions. If necessary, clean grill, using wire brush.

Set wrapped tortillas on one side of grill to warm over indirect heat.

Pat marinated shrimp dry with paper towels. Discard shrimp marinade. String shrimp evenly on skewers, alternating curve to opposite sides. Grill shrimp until almost opaque in center, about 2 minutes. Turn skewers and grill until shrimp are opaque in center but still moist, about 1 minute. Remove skewers, and add shrimp to platter of vegetables.

Open packets of warm tortillas and place cilantro sprigs on plate. Let people assemble their own.