Prep and Sauté: In a large skillet, heat olive oil over medium heat. Add the diced onion and garlic; sauté until soft and translucent (about 3-4 minutes). Add the ground beef to the pan, breaking it apart with a wooden spoon. Cook until browned and fully cooked (around 7-8 minutes). Drain excess grease, if necessary.
Season the Beef: Stir in Worcestershire sauce, paprika, oregano, salt, black pepper, and chili flakes (if using). Add the frozen mixed vegetables and sauté for 2-3 minutes until slightly softened. Add Rice and Liquids Stir in the uncooked rice, ensuring it’s well mixed with the beef and vegetables. Pour in the beef broth and tomato sauce. Bring the mixture to a gentle boil over medium-high heat.
Simmer: Reduce heat to low, cover with a lid, and simmer for 20-25 minutes. Stir occasionally to prevent the rice from sticking to the bottom. Continue cooking until the rice is tender and the liquid is mostly absorbed.
Add Cheese: Once the rice is cooked, sprinkle shredded cheddar cheese evenly over the top of the casserole. Cover with the lid for 3-5 minutes, allowing the cheese to melt completely.
Serve: Remove from heat and let the casserole rest for 5 minutes. This helps the flavors meld together. Garnish with fresh herbs like parsley or cilantro for added brightness, if desired.