Cook rice according to package directions until just al dente. Drain, if needed, and set aside.
Brown beef or bison in a large skillet until no pink remains; drain excess fat and add to rice in a large bowl along with beans.
Heat oil in the same skillet and cook peppers and onions until slightly softened, about 5 minutes; add to beef mixture.
Add all remaining ingredients to beef mixture except cheese and stir gently to mix well.
Pour beef mixture into a greased 13 x 9 baking dish and top with grated cheese.
Cover and bake at 375 until bubbly throughout and cheese has melted, about 40 minutes.
Let stand a few minutes before serving.
Top with fresh cilantro and avocado if desired.
Notes
If you desire a casserole that holds together more when serving, add ¼ cup of flour to the meat and vegetable mixture before pouring it into the baking dish.
Recipe by Cooking With MicheleĀ® at https://cookingwithmichele.com/2011/04/mexican-casserole-with-beef-and-rice/