Follow these simple steps to create a mouthwatering Cheesy Ground Beef Rice Casserole:

1. Preheat the Oven: Start by preheating your oven to 350°F (175°C).
2. Brown the Beef: In a large skillet over medium heat, cook the ground beef until browned. Drain any excess fat.
3. Sauté Onions and Garlic: Add the diced onion and minced garlic to the skillet. Sauté until the onion is translucent, about 3-5 minutes.
4. Mix in Seasonings: Stir in the Italian seasoning, salt, and pepper to taste. Combine well.
5. Add Rice and Liquid: Pour in the uncooked rice, diced tomatoes (with juice), and beef broth into the skillet. Stir to combine everything evenly.
6. Add Vegetables: If using, incorporate the frozen mixed vegetables and mix well.
7. Transfer to Baking Dish: Pour the beef and rice mixture into a greased 9×13 inch baking dish.
8. Top with Cheese: Sprinkle shredded cheddar and mozzarella cheeses evenly over the top of the mixture.
9. Bake: Place the baking dish in the preheated oven and bake for 30-35 minutes, or until the rice is tender and the cheese is bubbly.
10. Cool Before Serving: Remove from the oven and let it cool for 5-10 minutes before serving.

The simplicity of these steps makes this casserole accessible to cooks of all skill levels, resulting in a dish that is both satisfying and easy to pull together.