Cube Steak in the Slow Cooker

1 large onion, thinly sliced

1/3 cup all-purpose flour

1 tsp. garlic powder

1 tsp. onion powder

1/2 tsp. black pepper

6 (about 4 oz. each) beef cube steaks

1 Tbsp. canola oil

3 c. water, divided

1 envelope brown gravy mix

1 envelope mushroom gravy mix

1 envelope onion gravy mix