In a large skillet, cook the ground beef and chopped onion over medium-high heat until the beef is browned
Stir in the condensed cream of mushroom soup. This adds creaminess and flavor to the beef mixture.
In a greased 9x13-inch baking dish, spread out half of the frozen French fries in an even layer.
Spread the cooked beef and mushroom soup mixture evenly over the first layer of fries.
Sprinkle half of the shredded cheddar and mozzarella cheese over the beef layer.
Create another layer by placing the remaining frozen French fries over the cheese layer.
Finish by sprinkling the rest of the shredded cheddar and mozzarella cheese over the second layer of fries.