Finely chop the onion. Scrape peel from the ginger with a spoon, then coarsely chop ginger. In a food processor, blend the ginger and garlic together into a smooth paste, scraping the sides several times. (You'll have enough for this recipe plus extra for another use.) Set 2 tablespoons of ginger-garlic paste aside and refrigerate the remainder, covered, for up to one week.

Heat the oil in a Dutch oven over medium-high heat until shimmering. Add the cumin seeds, and when they start to sizzle, add the onion. Reduce heat to medium and cook, stirring occasionally, until onion turns golden brown, 12-14 minutes. Meanwhile, prepare the seasonings.

Combine the coriander, salt, ginger-garlic paste, turmeric, and garam masala in a small bowl. Add to browned onions in pot and stir well. Cook, stirring, over medium heat, until fragrant, about 30 seconds.

Add the tomatoes and stir to combine. Increase heat to medium-high and cook, stirring often, until liquid evaporates and masala turns into a loose paste, about 8 minutes.

Rinse the chickpeas in a colander and drain. Add to the pot and stir well to combine, then add the water. Cover and cook over medium-high heat for about 5 minutes to blend flavors.

Coarsely chop the cilantro. Stir the chana masala well, then sprinkle with cilantro and serve.