Heat the oil in a large skillet over medium heat. Add the squash, cumin, ½ teaspoon salt, and ¼ teaspoon pepper and cook, stirring occasionally, until tender, 11 to 13 minutes. Add the beans and ¼ cup water and cook until heated through, 1 to 2 minutes.
Top the tortillas with the squash and beans, onion, cheese, and parsley, dividing evenly. Serve with the lime wedges (if desired).