Preheat your oven to 350°F (175°C).
In a large skillet over medium heat, cook the ground beef until it browns. Drain any excess fat.
Add the chopped onion and minced garlic to the skillet. Sauté for about 3-4 minutes until the onion becomes translucent.
Stir in the frozen mixed vegetables and cook for an additional 2-3 minutes.
Mix in the canned diced tomatoes (with juice), beef broth, uncooked rice, oregano, salt, and black pepper. Stir everything well.
Let the mixture simmer for about 5 minutes, allowing flavors to meld together.
Transfer the beef and vegetable mixture into a greased 9x13 inch baking dish.
Spread the shredded cheddar cheese evenly over the top.
Cover the dish with aluminum foil and bake in the preheated oven for 30 minutes.
Remove the foil and bake for an additional 15 minutes, or until the cheese is bubbly and the rice is cooked through.
Remove from the oven and let it rest for 5 minutes before serving. Garnish with fresh parsley if desired.