Heat grill to high.
Wrap tortillas in aluminum foil and on the top rack of the grill while the steak is grilling.
Heat grill pan
over high heat. Brush steak with oil and season with salt and pepper on both sides. Grill on one side until golden brown and slightly charred, about 3 to 4 minutes. Turn the steak over and cook to medium-rare doneness, about 3 to 4 minutes longer. Let rest 5 minutes then slice against the grain into 1/4-inch thick slices.
Fill each tortilla with some lettuce, 3 to 4 pieces of meat, onion, grilled tomato salsa, sour cream
, and avocado