Cook the Potatoes: In a large pot, bring salted water to a boil. Add the diced potatoes and cook until tender, about 10-12 minutes. Drain and set aside.

Cook the Ground Beef: In a large skillet, heat olive oil over medium heat. Add the ground beef, chopped onion, and minced garlic. Cook until the beef is browned and the onion is soft, about 7-8 minutes. Drain any excess fat.

Add Vegetables and Seasoning: Stir in the frozen mixed vegetables, cream of mushroom soup, sour cream, dried thyme, salt, and pepper into the beef mixture. Cook for another 5-7 minutes until heated through and well combined.

Combine with Potatoes: Gently fold in the cooked potatoes into the beef and vegetable mixture, ensuring everything is evenly combined.

Assemble the Casserole: Preheat your oven to 350°F (175°C). Transfer the mixture into a greased 9×13-inch baking dish. Top with shredded cheddar cheese.

Bake: Bake for 20-25 minutes, or until the cheese is melted and bubbly. If you’d like a golden top, broil for 2-3 minutes at the end.

Serve: Let the casserole rest for 5 minutes before serving. Garnish with chopped parsley, if desired.