Steak Fajitas With Sweet Potato and Poblano

olive oil

large sweet potato (about 12 ounces), peeled and cut into 1⁄4-inch pieces

medium onion, thinly sliced

small poblano pepper, seeded and thinly sliced

kosher salt and black pepper

skirt steak, cut into 4 pieces

sour cream

to 2 teaspoons chopped canned chipotle chilies in adobo

small flour tortillas, warmed