Heat the chickpeas and strain just prior to adding other ingredients - Save the liquid.
Put 2 Tbsp. of the chopped onions, 1/2 tsp salt, green chili, ginger and lemon juice into a cup. Mix well and set aside.
Heat the oil in a heavy, wide pot. When hot, put in the remaining chopped onions. Stir and fry for 8 to 10 minutes or until onions have reddish brown spots.
Add the tomatoes continuing to fry for 5 to 6 minutes, mashing the tomatoes with the back of a slotted spoon.
Add coriander, cumin and turmeric to tomatoes/onion mixture.
Stir and cook for about 30 seconds.
Add drained chickpeas, 1 3/4 cup of their liquid, 2 tsp salt
Add Garam Masala and cayenne.
Stir to mix and bring to a simmer. Cover, turn heat to low and cook gently for 20 minutes. Stir a few times during this period. Add the mixture in the cup. Stir. Serve hot or lukewarm.