01 - Preheat the oven to 320°F (160°C) or set the slow cooker to low heat.
02 - Generously season lamb shanks with salt and black pepper on all sides.
03 - In a large Dutch oven or heavy ovenproof pot, heat olive oil over medium-high heat. Sear lamb shanks until browned on all sides, approximately 8 minutes total. Remove and set aside.
04 - Add chopped onions, carrots, and celery to the same pot and sauté for 5 to 7 minutes until softened. Add minced garlic and cook for an additional minute.
05 - Stir in tomato paste and cook for 1 minute. Pour in red wine, scraping the pot bottom to deglaze. Simmer for 2 minutes.
06 - Incorporate crushed tomatoes, stock, rosemary, thyme, bay leaves, and oregano. Stir to combine thoroughly.
07 - Nestle lamb shanks back into the pot with the sauce. Bring to a gentle simmer.
08 - Cover pot tightly and transfer to oven, cooking for 2.5 to 3 hours, or cook in slow cooker on low for 7 to 8 hours, until lamb is tender and falling off the bone.
09 - Remove lamb shanks and cover with foil to retain warmth. Skim excess fat from sauce and simmer uncovered on the stovetop for 10 to 15 minutes to thicken if desired.
10 - Plate lamb shanks and spoon sauce generously over. Garnish with fresh herbs as preferred.