Preheat oven to 350F degrees.
Add the ground beef and diced onions to a large pan and cook and crumble over medium heat until the meat is cooked through.
Drain excess grease.
Add ¾ cup water and taco seasoning.
Bring to a boil.
Reduce the heat and simmer for 5 minutes, stirring occasionally. Remove from heat.
To a 13x9 casserole dish, spread the refried beans in an even layer.
Top with sour cream, spreading out to the edges.
Top with cooked ground beef mixture, then with cheese.
Bake, uncovered, for 15 minutes, or until the cheese is hot and melted.
Remove from the oven and top with chips - return to the oven and bake for 5-8 minutes more or until the chips are toasty.
Add toppings and serve right away!