In a skillet over medium heat, cook ground beef and diced onion until fully browned. Drain excess grease.
Transfer the cooked beef and onion to a slow cooker.
Add taco seasoning, cheddar cheese soup, Rotel, chili beans, and water. Stir well to combine.
Cover and cook on low for 4 to 5 hours or on high for 2 to 3 hours.
To serve, place a generous handful of Fritos in a bowl, top with the taco mixture, and add shredded cheese, sour cream, and your favorite toppings.