In a large skillet over medium heat, add the ground beef and chopped onions. Cook until the beef is browned and the onions are translucent, about 5-7 minutes.
Once the beef is cooked, drain any excess fat. Stir in the taco seasoning mix and water. Let it simmer for about 5 minutes.
In a greased baking dish, spread the refried beans evenly across the bottom. Layer the seasoned beef mixture over the beans, pour the taco sauce on top, and sprinkle the tortilla chips evenly over everything.
Generously sprinkle the shredded cheddar cheese over the tortilla chips.
Preheat your oven to 350°F (175°C). Bake for 20-25 minutes, or until the cheese is melted and bubbly.
Once out of the oven, let it cool for a few minutes. Top with shredded lettuce and chopped tomatoes before serving.
