Preheat your oven to 400°F (200°C).

Grease a 9×13-inch baking dish or casserole dish to prevent sticking. You can also line it with parchment paper for easier cleanup.

In a large skillet over medium heat, cook the ground beef and diced onion until the beef is browned and the onion is soft (about 5-7 minutes). Make sure to break up the beef with a spoon as it cooks. Drain any excess grease.

Mix in the marinara sauce, Italian seasoning, and a pinch of salt and pepper in the skillet. Stir well and let it simmer for a couple of minutes.

Spread the beef and sauce mixture evenly in the prepared baking dish. Sprinkle 1 cup of shredded cheese over the mixture.

Arrange the frozen tater tots in a single layer on top of the cheese and beef mixture. Sprinkle the remaining 1 cup of cheese over the tater tots.

Bake the casserole in the preheated oven for 25-30 minutes until the tater tots are golden and crispy.

Optionally add mini pepperoni, olives, bell peppers, or any other favorite toppings during the last 5 minutes of baking.

Once done, remove from the oven and let it cool slightly before serving. Cut it into squares and dish it out on plates.