These slow cooker fajitas are amazing Flank steak is cooked in the crock pot with seasonings then served in tortillas with tomatoes and optional toppings. We used skirt steak in this recipe and the results were excellent. The flank steak is cut up and slow cooked to perfection with onions, peppers, garlic, and seasonings. Chopped fresh or canned tomatoes are also added to the beef mixture. Garnish the fajitas with fresh chopped cilantro, sour cream or guacamole, chopped tomatoes, and shredded cheese.