Combine all ingredients except the onions and water and place in a medium-sized bowl. Marinate for about 2 hours in the refrigerator or overnight.
When marinating is done, cut the onions and dump into the bottom of the slow cooker. Add the marinated steak and then pour on the water. Cover, and cook on medium low heat for around 6 hours until dinner. If you run out of water, pour in more.
Serve with the onions and some roasted vegetables on the side, on sandwiches, or reheat later for a sandwich!