Season lamb with salt, pepper, paprika, rosemary, and thyme, then brown in olive oil until deeply golden on all sides for extra flavor.
Add onions, carrots, celery, potatoes, and garlic to the crockpot, then stir in tomato paste, beef broth, Worcestershire sauce, balsamic vinegar, and bay leaves.
Place browned lamb over the vegetables, cover, and cook on low for 7–8 hours or high for 4–5 hours until the meat becomes fork tender.
Remove bay leaves, skim excess fat if needed, then stir in cornstarch slurry and cook uncovered for 20–30 minutes to thicken the sauce.
Garnish with parsley and black pepper before serving hot with mashed potatoes, rice, or crusty bread.