01 - Pat the lamb shanks dry with paper towels and season generously with salt and pepper on all sides.
02 - In a large heavy-based pot or Dutch oven, heat the vegetable oil over medium-high heat. Sear the lamb shanks on all sides until deeply browned, approximately 3-4 minutes per side. Remove from pot and set aside.
03 - Add the sliced onions to the same pot and sauté until golden brown and caramelized, about 10 minutes. Stir occasionally to prevent burning.
04 - Add the minced garlic and grated ginger to the pot. Cook for 1-2 minutes until fragrant, stirring constantly to prevent sticking.
05 - Stir in all ground spices (coriander, cumin, garam masala, turmeric, chili powder, black pepper) along with whole spices (bay leaves, cloves, cardamom pods, cinnamon stick). Toast for 1 minute, stirring constantly to release their aromatic oils.
06 - Add the chopped canned tomatoes and cook for 5 minutes, allowing them to soften and release their juices, forming a thick base.
07 - Return the seared lamb shanks to the pot. Pour in the stock and bring to a gentle simmer. Ensure the liquid nearly covers the shanks.
08 - Cover with a tight-fitting lid, reduce heat to low, and cook gently for 2.5 hours. Turn the shanks occasionally to ensure even cooking and tenderness.
09 - Remove the lid and stir in the yogurt, fresh tomatoes, and green chili if using. Simmer uncovered for another 45-60 minutes until the lamb is fork-tender and falling off the bone, and the sauce has thickened to a rich consistency.
10 - Skim any excess fat from the surface if desired. Taste and adjust seasoning with additional salt as needed.
11 - Transfer to serving plates, garnish generously with fresh chopped cilantro, and serve with lemon wedges on the side.