Heat the oil in a large skillet over medium heat.
Add the sweet potato, onion, poblano, ½ teaspoon salt, and ¼ teaspoon black pepper. Cook, tossing occasionally, until tender, 10 to 12 minutes.
Meanwhile, heat broiler. Season the steak with ½ teaspoon salt and ¼ teaspoon black pepper and place on a broilerproof rimmed baking sheet.
Broil the steak for 3 to 4 minutes per side for medium-rare. Let rest at least 5 minutes before slicing.
In a small bowl, combine the sour cream and chipotles. Fill the tortillas with the steak, vegetables, and chipotle sour cream.