Heat a medium skillet over high. Add oil to pan; swirl to coat. Pat tuna dry with a paper towel. Sprinkle tuna with salt and pepper. Add tuna to pan; cook 2 minutes on each side or until desired degree of doneness. Transfer tuna to a cutting board; cut cross the grain into 1/4-inch thick slices.
Warm tortillas. Divide tuna evenly among tortillas. Top each taco with 1 tablespoon salsa and 2 avocado slices. Serve immediately.