Season the lamb shanks generously with salt and pepper.
Heat olive oil in a skillet over medium-high heat and sear the lamb on all sides until browned.
Assemble in Slow Cooker:
Transfer seared lamb shanks to the slow cooker.
Add chopped onions, garlic, carrots, tomato paste, crushed tomatoes, broth, Worcestershire sauce, thyme, rosemary, and bay leaf. Stir gently to combine.
Cook:
Cover and cook on Low for 8 hours or High for 4–5 hours, until the lamb is fork-tender and the sauce is thick and savory.
Serve:
Remove bay leaf and herbs if using fresh stems.
Serve lamb shanks over mashed potatoes, creamy polenta, or with crusty bread to soak up the sauce.
