Preheat your oven to 375°F. Grease a 9x13 inch baking dish.
In a large skillet, cook the ground beef and diced onion over medium heat until the beef is browned and the onion is translucent. Drain excess fat.
Season with Montreal steak seasoning. Stir in ketchup, mustard, Worcestershire sauce, mushroom soup and condensed cheddar cheese soup. Simmer for 5 minutes.
Spread the cooked beef mixture evenly into the bottom of the prepared baking dish. Sprinkle with shredded cheddar cheese.
Arrange the frozen French fries on top of the beef mixture in a single layer. Bake in the preheated oven for 40-45 minutes or until the fries are golden brown and crispy.
Once done, remove from the oven and let it cool slightly before serving.
Serve the cheeseburger French fry casserole hot, with optional toppings such as diced tomatoes, pickles, lettuce, and additional ketchup and mustard if desired.
Video
Notes
If you use lean ground beef, add 1 tablespoon extra virgin olive oil to the skillet before adding the ground beef and diced vegetables.There is no need to thaw the fries. I used krinkle fries because I like the way they look, but you can use regular french fries if you prefer.Be sure to bake the french fries until they are hot and crispy.