1. Thaw fish if frozen. Rinse and pat dry with paper towels. Preheat grill to medium-high.
2. Tear off an 18x18-inch sheet of Reynolds Wrap(R) Heavy Duty Aluminum Foil. Place onion in the center of the sheet. Top with salmon. Drizzle with the olive oil and sprinkle with the salt and black pepper. Top with lemon slices. Bring up foil sides. Double-fold top and ends to seal packet, leaving room for heat circulation inside.
3. Stack flatbreads; wrap tightly in heavy duty aluminum foil.
4. Grill salmon packet over medium-high heat in covered grill 12 to 14 minutes or until fish begins to flake when tested with a fork and vegetables are tender.
5. Add the flatbread packet to the grill for the last 5 minutes of cooking to warm through, turning once. Remove all from the grill.
6. Open packets carefully by cutting along top folds with a sharp knife, allowing steam to escape. Then open top of the foil. Discard lemon slices. Use two forks to pull the salmon apart into chunks.
7. Assemble sandwiches by topping pita with the salmon, onions, lettuce, and tomatoes. Fold in half to serve. In a small bowl, mix together the yogurt, basil, and dill. Serve over pita sandwiches.