Preheat oven to 350 degrees F (175 degrees C).

Place the ground beef and onion in a skillet over medium heat. Cook and stir until beef is evenly brown and onion is tender. Drain grease. Mix in soup, and continue cooking until heated through.

In a bowl, mix the marinara sauce, tomato sauce, and water. Spread 1/3 of the mixture across the bottom of a 9x13 inch baking pan. Fill each tortilla with about 2 tablespoons beef mixture and 2 slices cheese food (reserving enough cheese food slices for topping). Tightly roll each tortilla. Arrange tortillas in the pan in 2 layers, and cover completely with the remaining sauce mixture. Top with remaining cheese food.

Cover with aluminum foil, and bake 45 minutes in the preheated oven, until bubbly.