1. Preheat your oven to 350°F (175°C). Lightly grease a 9×13-inch baking dish with cooking spray or a little olive oil.
2. In a large skillet, heat the olive oil over medium heat. Add the chopped onion and sauté until translucent, about 3-4 minutes. Add the minced garlic and cook for another 30 seconds until fragrant.
3. Add the ground beef to the skillet. Break it apart with a wooden spoon and cook until browned and cooked through, about 7-8 minutes. Drain any excess fat if necessary.
4. Stir in the Worcestershire sauce, dried thyme, salt, and pepper. Mix well to combine all the flavors.
5. In a large mixing bowl, combine the uncooked rice, beef broth, cream of mushroom soup, frozen mixed vegetables, and the cooked beef mixture. Stir until everything is evenly mixed.
6. Pour the mixture into the prepared baking dish, spreading it out evenly.
7. Cover the dish tightly with aluminum foil and bake for 45 minutes. This allows the rice to cook fully and absorb all those rich flavors.
8. After 45 minutes, carefully remove the foil and sprinkle the shredded cheddar and mozzarella cheeses evenly over the top.
9. Return the casserole to the oven, uncovered, and bake for an additional 10-15 minutes, or until the cheese is melted and bubbly with a golden edge.
10. Remove from the oven and let it rest for 5 minutes before serving. This little pause lets the casserole set and makes it easier to scoop out perfect portions.

One tip I’ve learned after many family dinners is that letting the casserole rest is key. It prevents the cheese from sliding off and gives everyone a moment to gather around the table, ready to dig in.