Warm a large non-stick skillet over medium heat. Add the ground beef, sprinkle with salt and pepper. Cook the beef by browning it and breaking it up with a spatula as it cooks.
While the beef is cooking, prepare your rice using the package instructions or my method linked in the post.
Once the beef is completely cooked and no pink remains, use a slotted spoon to transfer the beef to a plate lined with paper towels. Drain most of the fat from the pan and return it to the heat. Add the diced onions to the pan and cook them, stirring frequently until they soften, about 3-5 minutes.
Add the minced garlic to the pan and stir for 60 seconds more. Add the cooked beef back into the pan and stir.
Pour the crushed tomatoes and salsa into the beef mixture and stir well. Next, add in the can of beans and cooked brown rice. Stir well again to combine.
Turn the oven on to 350 and spray a 9x9 oven-safe casserole dish. Transfer the beef mixture to the prepared casserole dish.
Top the beef mixture with the shredded cheese and sprinkle the diced green pepper over the cheese.
Place the dish in the oven and bake for 25 minutes. Turn on the broiler and broil for 2-3 minutes until the cheese is bubbling.
Serve warm with sides of avocado, guacamole, and/or sour cream.
Store any leftovers covered in the fridge for up to 3 days.