Heat the vegetable oil in a large pot over medium heat. Add the chopped onions and sauté until they turn golden brown, about 5-7 minutes.

Stir in the minced garlic, ginger, and green chilies. Cook for another 2-3 minutes until fragrant.

Add the chopped tomatoes and cook until they soften, about 5 minutes.

Mix in the turmeric powder, red chili powder, coriander powder, cumin powder, and salt. Stir well to combine and cook for 2 minutes.

Add the mutton pieces to the pot, stirring to coat them in the spice mixture. Cook for about 5 minutes, allowing the meat to brown slightly.

Pour in enough water to cover the mutton (about 2-3 cups) and bring to a boil. Reduce the heat to low, cover, and simmer for 1.5 to 2 hours, or until the mutton is tender. Stir occasionally and add more water if necessary.

Once the mutton is tender, uncover the pot and increase the heat to medium-high. Cook for an additional 10-15 minutes to reduce the sauce to your desired consistency.

Stir in the garam masala and lime juice. Cook for another 2 minutes.

Garnish with chopped cilantro before serving.