Heat your oven to 350°F (175°C). Lightly coat a 9×13-inch baking dish with cooking spray and set it aside.

Warm a large skillet or Dutch oven over medium. Add the ground beef and diced onion, breaking the meat into pieces as it cooks. Continue until the beef is browned and the onion is soft, about 10 minutes, then drain any excess fat.

Stir in the minced garlic and cook just until fragrant, about 30 seconds. Remove the pan from the heat to prevent the garlic from browning.

Mix in the cream of celery soup and beef stock, then add the garlic powder, onion powder, Italian seasoning, paprika, kosher salt, and black pepper. Stir until the mixture is smooth and evenly seasoned.

Fold in the instant rice and the frozen mixed vegetables, stirring until they are fully combined with the beef and sauce.

Transfer the casserole mixture into the prepared baking dish and spread it evenly. Sprinkle the shredded cheddar on top, cover with nonstick foil, and bake for about 45 minutes or until the casserole is bubbling and the cheese has fully melted.

Remove the foil and place the dish under the broiler for a few minutes to lightly brown the cheese—watch closely to avoid burning. Optionally garnish with fresh or dried parsley, then serve hot.