Cook the rice and set it aside to cool.
Brown the beef until no longer pink on the stovetop. Add the onion and garlic. Stir in the other ingredients, including the rice. If making into a freezer meal, add this mixture into a large resealable bag, remove the excess air, and freeze. On the day of cooking, take out of the freezer and thaw.
Wash and cut the tops off the bell peppers and seed them. Fill each one with the filling. Sprinkle each with cheese. Place on a greased cookie sheet with a rim or baking pan and bake at 350 degrees for 35-40 minutes.
*I have not been able to find a gluten-free vegetarian ground beef substitute so making it with the meatless ground round means that it won't be gluten-free. **ensure that the taco seasoning you use is gluten-free. Most are not. I use VE which is gluten-free or I have found a tex mex seasoning that is also gluten-free. Alternatively, you can make your own.
The filling is pretty delicious on its own and even better with some hot sauce sprinkled on so if you have any leftover filling when you're stuffing the peppers, you can eat just the filling.
I really do recommend making this in multiple batches and freezing as then you will only have to brown the meat, make the rice and make the filling once.