Beefy Hash Burgers

1 pound ground beef, browned and drained
1 pkg hash brown potatoes, chunk style
2 cups hot water
1/2 cup ketchup
2 Tbsp mustard
1 Tbsp dried chopped onion
1 can chicken gumbo soup
1 cup shredded cheddar cheese
12 Hamburger Buns

Stir together all ingredients except cheese and buns in large skillet. Heat to boil. Simmer uncovered 15-20 minutes. Stir in cheese. Fill buns.