Step 1: Prepare the Beef Mixture

• Heat a large skillet over medium-high heat. Add the ground beef and cook until browned, breaking it apart as it cooks (about 6-8 minutes). Drain any excess grease.
• Add the diced onion, bell pepper (if using), and garlic to the skillet. Cook for another 4-5 minutes until the vegetables are softened and fragrant.
• Stir in the taco seasoning and diced tomatoes with green chilies (including their liquid). Allow the mixture to simmer for 2-3 minutes until the flavors meld.

Step 2: Cook the Rice

• While the beef mixture is cooking, prepare the rice. In a medium pot, bring 2 cups of beef broth or water to a boil. Stir in the uncooked rice, reduce the heat to low, cover, and simmer for 15-20 minutes or until the rice is tender and the liquid is absorbed.
• Fluff the rice with a fork once it is fully cooked.

Step 3: Combine Beef and Rice

• Once the rice is cooked, add it to the skillet with the seasoned beef mixture. Stir everything together until well combined.
• Preheat your oven to 350°F (175°C).

Step 4: Assemble the Casserole

• In a large mixing bowl, combine the cheddar cheese soup, half of the shredded cheddar cheese, and half of the shredded Monterey Jack cheese.
• Add the beef and rice mixture to the cheese mixture and stir until everything is evenly combined and coated in the cheesy sauce.

Step 5: Bake the Casserole

• Transfer the mixture to a greased 9×13-inch baking dish, spreading it out evenly. Sprinkle the remaining shredded cheese on top.
• Cover the dish with aluminum foil and bake in the preheated oven for 20 minutes.
• After 20 minutes, remove the foil and bake for an additional 10-15 minutes until the cheese is bubbly and golden.

Step 6: Add the Toppings

• Once the casserole is out of the oven, sprinkle the crushed tortilla chips on top for added crunch.
• Scatter the shredded lettuce and diced tomatoes over the casserole for a fresh, bright topping.

Step 7: Serve with Salsa and Sour Cream

• Slice the casserole into squares or scoop out individual servings.
• Serve each portion with a dollop of salsa and a spoonful of sour cream to give it that classic taco finish.