2. Chop the avocado and toss it with the remaining lime juice, mango, red pepper and scallions. (This can be made in advance and stored in the refrigerator for up to 1 day.)
For the fish:
3. Preheat the grill.
4. Brush the fillets with oil and season generously with salt and pepper.
5. Grill the fillets on both sides until just cooked through, about 5 minutes per side. (Thin fillets take less time, thicker fillets take more.) Cool slightly and cut into 1-inch pieces.
6. Meanwhile, separate the tortillas into 2 stacks, wrap them in foil and warm them on the grill while the salmon is cooking.
To serve the tacos: 7. Fill the tortillas with fish, lettuce, tomatoes and mango-avocado salsa. Serve 2 tacos per person with lime wedges on the side.