Drain chickpeas and wash well.
Blend the tomatoes, green chilies and ginger to make a puree.
Heat the oil in a saucepan. Test the heat by adding one cumin seed to the oil; if seed cracks right away, oil is ready. Add the asafetida and cumin seeds. When cumin seeds crack, add the gram flour and stir-fry for a minute.
Add the tomato puree, coriander powder, turmeric, and red chili powder. Cook about four minutes on medium heat. The tomato mixture will separate from the oil and reduce to about half in quantity.
Add chickpeas, salt, and one cup of water. Cook, covered, for seven to eight minutes on medium heat. Press the chickpeas with a spatula to soften. Add more water as needed to keep the gravy consistency to your liking, and let it cook on low heat a few more minutes.
Add the garam masala and cilantro. Let it cook for another minute.
Garnish with thin tomato slices.