Preheat your oven to broil on high.
Spread the Alfredo sauce evenly across the bottom of a 9x13-inch baking dish.
Add the cooked spaghetti noodles and toss them gently until coated in the Alfredo sauce.
In a separate bowl, combine the browned ground beef with the marinara sauce.
Spread the meat sauce evenly over the spaghetti.
Sprinkle the mozzarella cheese over the top.
Broil on high for 2 to 5 minutes, or until the cheese is melted, bubbly, and lightly golden. Watch carefully to prevent burning.
Let the casserole cool for a few minutes before serving.
