Step 1 Preheat your oven to 375°F (190°C). While the oven heats, lightly grease a 9×13-inch baking dish with nonstick cooking spray, butter, or a thin film of oil. This prevents the creamy beef mixture from sticking and makes serving and cleanup easier. Set the prepared dish aside. Having the oven fully preheated before the casserole goes in ensures even cooking and proper crisping of the tater tots.

Step 2 Place a large skillet over medium-high heat. Add the ground beef and the diced onion together. Cook for 6 to 8 minutes, using a wooden spoon or spatula to break the beef into small crumbles as it browns. Continue cooking until the beef is no longer pink and the onion has softened and become translucent. If a significant amount of grease has rendered, carefully drain most of it, leaving a small amount in the pan for flavor. Proper browning develops deep savory notes that form the foundation of the entire casserole.

Step 3 Add the minced garlic, chili powder, smoked paprika, garlic powder, onion powder, a generous pinch of salt, and several grinds of black pepper to the skillet. Stir continuously and cook for about 1 minute, just until the garlic becomes fragrant and the spices bloom in the residual fat. This brief cooking step releases the essential oils in the spices and prevents any raw garlic flavor from lingering. Taste a small amount of the mixture at this stage and adjust seasoning if needed, keeping in mind that the soup and cheese will add additional salt later.

Step 4 Reduce the heat to medium-low. Stir in the well-drained diced tomatoes, the entire can of cream of mushroom soup, and the cup of sour cream. Mix thoroughly until the sauce is smooth, creamy, and evenly coats the beef and onions. The mixture should look rich and cohesive. If it appears too thick, you may add a splash of milk or water, though this is rarely necessary. Once everything is well combined, remove the skillet from the heat. The residual warmth will keep the mixture spreadable.

Step 5 Transfer the creamy beef mixture into the prepared 9×13-inch baking dish. Use a spatula to spread it into an even layer that reaches the corners. Sprinkle ½ cup of the shredded cheddar cheese and all of the Monterey Jack cheese evenly over the beef layer. This cheese layer will melt into the sauce and create gooey pockets throughout the casserole.

Step 6 Arrange the frozen tater tots in a single, even layer over the cheese and beef mixture. Place them close together so they cover the surface completely; this creates the signature crispy topping. Do not thaw the tots beforehand—using them frozen helps them stay firm and crisp during baking rather than becoming soggy.

Step 7 Place the uncovered casserole in the preheated oven and bake for 35 to 40 minutes. The exact time depends on your oven and how golden you prefer the tots. Look for the tater tots to turn a deep golden brown and become crispy on the edges, while the sauce underneath bubbles gently around the sides. If the tots brown too quickly, you can loosely tent the dish with foil for the last portion of baking, though this is usually unnecessary.

Step 8 Remove the casserole from the oven and sprinkle the remaining ½ cup of shredded cheddar cheese evenly over the hot tater tots. Return the dish to the oven for an additional 5 to 8 minutes, just until the cheese is fully melted, bubbly, and beginning to brown in spots. This final cheese layer adds an extra dimension of richness and visual appeal.

Step 9 Carefully remove the casserole from the oven. If using, sprinkle the chopped fresh parsley over the top for color and a touch of freshness. Allow the dish to rest for 5 minutes before serving. This resting period lets the sauce thicken slightly and makes scooping cleaner portions easier. Serve hot directly from the baking dish.