Peel and finely chop the onions, drain and rinse the chickpeas and finely slice the green chillies. Heat the oil in a saucepan over a medium heat and add the mustard seeds; once they’re crackling, add the asafoetida. Stir in the onions and fry until transparent and turning golden at the edges. Chop and add the tinned tomatoes, then cook for another 5 minutes, before adding the ginger, garlic and green chilli pastes, the red chilli powder, dhana jeera, sugar (if using), and a pinch of sea salt. Keep stirring and cook for further 5 minutes. Stir the chickpeas into the pan. Add 250ml water to make a thick sauce. Place the lid on the pan, lower the heat and simmer for 5 to 7 minutes. Pick and finely chop the coriander, then sprinkle on top along with the garam masala and finely sliced green chillies, to serve.