In a skillet, heat oil over medium-high heat. Brown beef in batches, adding more oil if necessary. Transfer with a slotted spoon to slow cooker stoneware.

Reduce heat to medium and add onions to pan. Cook until soft and add garlic, cinnamon and allspice, cooking for 1 minute. Add vinegar, tomato sauce, sugar and bay leaf. Stir to combine.

Pour mixture over meat and cook on low for 8-10 hours or on high for 4-5 hours until beef is tender.

Add feta cheese and cook on high for 10 minutes. Discard bay leaf. Spoon over hot buttered noodles or cooked (mashed, boiled, roasted) potatoes.