Stir flour, salt, garlic powder and ground mustard together in a bowl.
Dredge cube steaks in flour.
Brown in skillet in vegetable oil.
Remove and place steaks in crockpot.
Add onion to skillet and cook a few minutes.
Stir gravy mix and water together. Pour into skillet, scraping up the browned bits.
Pour gravy and onions over meat in crockpot.
Cook on low 7-8 hours or high 5-6 hours.