Preheat your oven: Start by setting your oven to 375°F (190°C). This will ensure it's nice and hot by the time your casserole is ready to bake.

Cook the ground beef: In a large skillet over medium heat, brown the ground beef until fully cooked. Make sure to break it apart as it cooks. Once browned, drain any excess fat and set the beef aside.

Sauté the onions: In the same skillet, add the chopped onion and sauté for about 2-3 minutes, until it’s soft and translucent. This will bring out its natural sweetness and flavor.

Mix the casserole ingredients: In a large mixing bowl, combine the cooked ground beef, sautéed onions, frozen mixed vegetables, cooked pasta, cream of mushroom soup, garlic powder, dried oregano, salt, and pepper. Stir everything together until well combined.

Transfer to a baking dish: Pour the mixture into a greased 9x13-inch baking dish. Use a spatula to spread it evenly, ensuring all ingredients are evenly distributed.

Add cheese: Sprinkle the shredded cheddar cheese evenly over the top of the casserole. For extra cheesy goodness, you can add a bit more cheese if desired.

Bake the casserole: Place the dish in the preheated oven and bake for about 20-25 minutes or until the cheese is melted and bubbly. You’ll know it’s ready when the cheese is golden and the casserole is heated through.

Serve and enjoy: Once out of the oven, let the casserole cool for a few minutes before serving. You can garnish it with fresh parsley for a touch of color, but it's just as delicious on its own!