Directions

1. Pierce the flank steak all over with a fork, and place into a large resealable plastic zipper bag. Mix the vegetable oil, lime juice, ranch dressing mix, cumin, and black pepper in a bowl, and pour over the flank steak. Force air out of the bag, seal, and refrigerate at least 6 hours.
2. Preheat an outdoor grill for medium-high heat, and lightly oil the grate.
3. Remove the flank steak from the marinade, and shake to remove excess marinade. Grill the steak until it shows good grill marks and the inside is the desired degree of doneness, about 10 minutes. Baste each side with marinade, taking care to cook the marinade onto the outside of the steak. An instant-read thermometer inserted into the middle of the steak should read 130 degrees F (54 degrees C) for medium-rare.
4. Allow the steak to rest for about 10 minutes before slicing thinly on the diagonal. While steak is resting, grill the onion and green pepper slices until they are starting to brown, about 3 minutes per side.
5. To serve, wrap sliced steak with grilled onion and green pepper in tortillas.