Heat the oil in the pan, and brown the onions to a light brown on a medium heat.
Turn the heat to low and add the cumin seeds, mustard seeds, curry leaves, ground coriander, salt , chilli powder, garlic and ginger and stir through with the onions. Be careful that the garlic and ginger does not burn.
Add the tomatoes and stir through. Let it cook for 2 minutes or so.
Next add the drained chickpeas and water, stir through and cover the pan with the lid. Let the chickpeas simmer for 10 minutes, until the chickpeas are soft. Check the chickpeas aren't sticking to the pan and stir at regular intervals during this time. If you feel the colour of the chickpeas looks too light, add a tablespoon of tomato puree and stir through.
If you want the chickpeas to be less saucy, leave the lid off the pan and cook for a few more minutes. You know the curry is ready when you see the oil separate from the chickpeas.
Finally add the tamarind sauce and garam masala and stir through. Finish with finely chopped coriander and serve with rice or roti/ chapati and enjoy.