Combine ground beef and onion in a large skillet over medium-high heat. Cook and stir until meat is well browned and onion is soft. Drain grease.
Cut each French roll into quarters. Spread the processed cheese sauce on cut sides of each piece; place on a baking sheet. Evenly spoon the cooked beef onto the cheese topped rolls. Top each roll with a dab of ketchup.
Bake in preheated oven until rolls are crisp and filling is hot, about 20 minutes.
