01 - Preheat the oven to 320°F or set the slow cooker to low.
02 - Generously season the lamb shanks with salt and black pepper on all sides.
03 - Heat olive oil in a large Dutch oven or heavy-based ovenproof pot over medium-high heat and brown lamb shanks on all sides for about 8 minutes. Remove and set aside.
04 - Add onions, carrots, and celery to the same pot and cook for 5 to 7 minutes until softened, then stir in minced garlic and sauté for 1 minute more.
05 - Stir tomato paste into the vegetables and cook for 1 minute. Pour in red wine and scrape the bottom of the pot to deglaze. Simmer for 2 minutes.
06 - Combine crushed tomatoes, stock, rosemary, thyme, bay leaves, and oregano into the pot; stir thoroughly.
07 - Nestle the lamb shanks back into the sauce and bring to a gentle simmer.
08 - Cover tightly and transfer to the oven to cook for 2.5 to 3 hours, or cook on low in a slow cooker for 7 to 8 hours, until the meat is tender and falling from the bone.
09 - Remove lamb shanks and keep warm covered with foil. Skim excess fat from the sauce and simmer uncovered on the stovetop for 10 to 15 minutes to thicken, as desired.
10 - Plate the lamb shanks with sauce spooned over, garnishing with fresh herbs if preferred.