In a large mixing bowl, combine ground beef, breadcrumbs, milk, onion soup mix, and dried thyme. Mix until just combined.

Form the mixture into 8 equal-sized patties and set aside.

Layer the sliced onions evenly on the bottom of a slow cooker.

Heat olive oil in a large skillet over medium-high heat. Dredge each patty lightly in flour and brown on both sides, working in batches if necessary.

Place the browned patties on top of the onions in the slow cooker, stacking them slightly if needed.

In a separate bowl, whisk together the cream of chicken soup, water, and au jus mix until smooth.

Pour the sauce mixture evenly over the patties in the slow cooker.

Cover and cook on low for 4 to 5 hours, or until the beef is fully cooked and tender.