Heat the oil in a large pan over medium heat until it becomes hot.
Once the oil reaches the desired temperature, sauté the ginger and garlic paste for 1-2 minutes.
Add the lamb to the pan and cook on high heat for 10 minutes until the meat changes colour.
Pour in the water, cover the pan with a lid, and simmer over medium heat for 40-45 minutes. This will allow the mutton to cook 80% and most of the water to evaporate.
Slice the tomatoes in half and place them face down in the pan. Cover with a lid and cook for 5 minutes.
Using tongs, remove the skin from the tomatoes and gently mash them.
Add the green chillies, salt, and black pepper to the pan and continue cooking for 15 minutes.
Once the oil separates, your curry is ready.
Serve immediately with homemade naan bread on the side and enjoy!