Preheat the Oven: Preheat the oven to 375°F (190°C). Grease a 9×13-inch baking dish.

Cook the Ground Beef: In a large skillet, heat olive oil over medium heat. Add the ground beef and cook, breaking it apart, until browned and fully cooked, about 6-8 minutes. Drain any excess fat.

Add Vegetables and Seasoning: Add the chopped onion and minced garlic to the skillet. Cook for 3-4 minutes until softened. Stir in the dried thyme, salt, and pepper.

Make the Creamy Sauce: Reduce the heat to low and add the cream of mushroom soup and sour cream. Stir to combine and cook for another 2-3 minutes until the sauce is heated through.

Combine with Pasta: Add the cooked pasta to the skillet and stir to combine with the creamy beef mixture.

Assemble the Casserole: Transfer the mixture into the prepared baking dish. Top with shredded cheddar and mozzarella cheese.

Bake: Bake for 20-25 minutes, or until the cheese is melted and bubbly.

Serve: Remove from the oven and garnish with chopped parsley, if desired.