Mix mutton pieces with all the marinade ingredients and keep aside for 1 hour.
In a pressure cooker, mix the marinated mutton pieces with 1 cup water (100 ml) and pressure cook for 35 minutes or until they soften (reduce the heat after 3rd whistle and cook on a low to medium heat for 25 minutes). Allow the cooker to cool naturally. Open the cooker and carefully remove cooked mutton pieces. You may get half cup mutton stock. Reserve it for another dish.
Mix coconut bits / thengakothu with turmeric powder and salt and keep aside for half an hour.
Heat oil in a pan and shallow fry marinated coconut bits until golden in colour, crisp and fragrant. Maintain low to medium heat.
Heat oil in a pan. Add sliced onions / shallots and fry till golden brown and crisp.
Add curry leaves and slit green chilli. Saute well for 2-3 minutes. Add shallow fried coconut bits and stir well.
Add cooked mutton pieces, adjust salt to taste and sprinkle 1/4 tsp pepper powder if required. Mix all the ingredients well. Cover with a lid and cook on low heat for 10-12 minutes.
Open the lid and stir well on low heat for 5-7 minutes.