Heat oil in a non-stick pan and brown the lamb pieces on all sides before setting them aside.
Fry mustard seeds in the same pan until they pop, then add onions and fry until golden-brown.
Blend garlic and ginger with a splash of water to create a smooth paste.
Add the paste to the onions and cook until the water evaporates and the mixture turns golden.
Stir in salt, sugar, coriander, cumin, turmeric, and chilli powder for thirty seconds.
Add pureed tomatoes and 100ml water, then simmer until the liquid reduces and the sauce dries out.
Mix dumpling ingredients in a bowl to form a semi-soft dough.
Roll the dough into three sausages and pinch off pieces to form eighteen smooth balls.
Stir in coconut milk, lemon juice, remaining water, and sweet potatoes, simmering for six minutes before adding dumplings.
Cover and simmer for seven minutes, then add the lamb and chickpeas and cook until done.
Stir in fresh coriander and garam masala immediately before serving.