Heat a medium, heavy-bottomed pan over medium-high heat. Once hot, heat the oil and add the cumin seeds and onion. Sauté for 7-8 minutes, until golden. If the mixture gets dry, deglaze with 1-2 tablespoons of water.
Add the garlic, ginger, and green chili pepper and sauté for another 2-3 minutes. Deglaze the pan with a tablespoon of water (if needed), and add all the spice powders. Give it a few stirs to roast the spices, and then add the tomatoes. Continue to sauté for another 2-3 minutes. Mix in the chickpeas, baking powder (if using), salt, and 2 cups of water.
Raise the heat to high to bring to a boil, then reduce the heat to medium, cover and let cook for 25-30 minutes, until the chickpeas are very tender.
Uncover and raise the heat to high. Use a wooden spatula to slightly crush the chickpeas. Sauté for another 2-3 minutes to desired consistency. Taste and adjust salt and seasoning. Turn off the heat and add the garam masala or chaat masala, lemon juice, and cilantro leaves. Sprinkle with julienned ginger and black pepper, if desired.