We adapted this recipe from several we found online and were very pleased with the results. We were able to warm up the filling as left overs for several meals.
2 lb Beef Roast
2 cups beef broth (mix 2 cups water with 2 teaspoons beef boulion)
1/2 cup diced onion
2 cloves garlice diced
1 diced green or red pepper (I don't like peppers, so these were left out)
2 teaspoons cumin
1 teaspoon cillantro
1/2 teaspoon ground coriander
1/2 teaspoon ground pepper
Serve on warm tortillas with rice, cheese, and lettuce.