In a large mixing bowl, combine the yogurt, ginger, garlic, turmeric, red chili powder, and Rogan Josh spice mix. Add salt to taste and mix well to form a marinade.

Add the lamb chunks to the marinade, ensuring each piece is well-coated. Cover the bowl and let it marinate in the refrigerator for at least 2 hours, or overnight for best results.

Heat the vegetable oil in a large, heavy-bottomed pot over medium heat. Add the sliced onions and sauté until they are golden brown, stirring occasionally to prevent burning.

Add the marinated lamb to the pot, cooking for about 5-7 minutes until the meat is browned on all sides.

Pour in the water and bring the mixture to a boil. Once boiling, reduce the heat to low, cover the pot, and let it simmer for 1.5 to 2 hours, or until the lamb is tender.

Stir occasionally and add more water if necessary to prevent the curry from sticking to the bottom of the pot.

Once the lamb is tender, taste and adjust the seasoning if needed.

Garnish with fresh cilantro before serving.