Thaw fish, if frozen. Rinse fish; pat dry. Place fish in a resealable plastic bag set in a shallow dish.
In a small bowl, combine lemon juice, shallots, oil, dill, garlic, salt, and pepper. Pour over fish in bag. Seal bag. Marinate in the refrigerator for up to 1 hour, turning the bag occasionally. Remove salmon from marinade, reserving marinade.
Grill fish on the well-greased grill rack of an uncovered grill directly over medium coals for 4 to 6 minutes per 1/2-inch thickness of fish or until fish flakes easily when tested with a fork, brushing with reserved marinade and gently turning halfway through grilling. (Discard any remaining marinade.) (For a gas grill: Preheat grill. Reduce heat to medium. Place fish on grill rack over heat. Cover and grill as above.)
Transfer fish to a cutting board. Using a fork, flake fish into bite-size pieces.
Spread Garlic-Lemon Mayonnaise on each tortilla. Top with lettuce and salmon pieces. Roll up; secure with toothpicks, if necessary. If you like, serve with lemon wedges.
In a small bowl, stir together mayonnaise,celery, dill, lemon peel, green onion and garlic. Makes about 1/2 cup.