In a large shallow skillet, or cast iron pan, Heat rendered bacon grease. Add onion to the pan. Fry until barely brown. Add cabbage and cooked rutabagas. Let fry. Stir often.
In a separate skillet, re-warm and fry chopped corned beef in remaining bacon grease. Let it get slightly browned and heated through.
Season veggie mixture with garlic seasoning. Add heated corned beef to large skillet and veggies. Stir and sauté briefly to combine. Serve with cooked egg if desired.