Heat grill to high (450° to 550°). Mix seasonings in a small bowl. Put halibut on a rimmed baking sheet; coat with oil. Sprinkle with seasonings. Thread fish on 6 to 8 slender metal skewers. Oil cooking grate, using tongs and a wad of oiled paper towels.
Grill fish, covered, turning once, until just cooked through, 3 to 4 minutes total. Fill tortillas with lettuce, fish, and salad. Serve with yogurt sauce.
*If tortillas are very thin, buy double the amount and stack 2 per taco.
Note: Nutritional analysis is per taco with 1 tbsp. sauce.