Heat the oil in a large pot over medium heat. Add the lamb cubes and brown them on all sides, then remove and set aside.
Add the onion to the same pot and cook until softened. Stir in the garlic, ginger, and green chili.
Sprinkle in the cumin, coriander, and turmeric. Cook the spices for one minute until fragrant.
Return the lamb to the pot along with the potatoes. Pour in the lamb broth and bring to a simmer.
Cover and cook for 45 minutes until the lamb is tender and the potatoes are soft.
Stir the yogurt into the pot a spoonful at a time, then add half the cilantro and all the mint. Simmer uncovered for 5 minutes to thicken the gravy.
Season with salt and pepper. Scatter the remaining cilantro over the top before serving.