Start by preheating your oven to 350 degrees F. Lightly grease a large casserole dish (9×13 inch or similar) with nonstick spray and set it aside. If your rice or chosen grain isn't cooked, now is the time to prepare it. Quinoa is a quick alternative if you're short on time, and instant brown rice is also a convenient option.

In a large Dutch oven or deep skillet, heat the olive oil over medium-high heat. Add the chopped onion, green bell pepper, and red bell pepper. Sauté the vegetables for about 5 minutes, until they begin to soften.

Next, add the ground beef, chili powder, cumin, salt, black pepper, and cayenne pepper. Cook the mixture, breaking up the beef as it browns. Continue cooking until the beef is thoroughly cooked and no pink remains, approximately 4 to 5 minutes. Stir in the minced garlic and cook for an additional minute, just until the garlic becomes fragrant.

Remove the skillet from the heat and stir in the cooked rice and Greek yogurt until the mixture is well combined. Taste the mixture and adjust the seasonings if necessary.

To assemble the casserole, spread the refried black beans in an even layer at the bottom of the prepared casserole dish. Sprinkle 1/4 cup of the grated cheddar cheese and 1/4 cup of the grated mozzarella cheese over the beans.

Layer the drained tomatoes with green chiles on top of the cheese. Spoon the rice and ground beef mixture over the tomatoes, spreading it out evenly.

Finish by sprinkling the remaining 1/2 cup of cheddar cheese and 1/2 cup of mozzarella cheese over the top.

Bake the casserole uncovered for about 15 minutes, or until the cheese is melted and the dish is heated through. Switch the oven to broil and cook for an additional 3 to 4 minutes, just until the cheese is lightly browned. Keep a close eye on it to prevent burning.

Once baked, allow the casserole to rest for 5 minutes. Garnish with chopped cilantro and green onions before serving. Enjoy this hearty and flavorful Mexican casserole!