In a large mixing bowl, combine ground beef, onion soup mix, breadcrumbs, and milk together. Divide meat mixture into 8 patties and shape into oval-shaped patties. Dredge in flour and set aside.

In a skillet, heat the olive oil. Brown the patties in the skillet, a few at a time, for just a minute on each side. Transfer to slow cooker, stacking if needed.

In another mixing bowl, whisk together the mushroom soup, au jus mix, and water. Pour mixture over the patties in the slow cooker.

Cover and cook on low for 6 hours or high for 4 hours.