Step 1

Chop three-quarters of onion coarse; reserve remaining quarter for garnish. Cut cilantro stems into 1-inch lengths. Process chopped onion, cilantro stems, ginger, garlic, and half of serranos in food processor until finely chopped, scraping down sides of bowl as necessary, about 20 seconds. Combine onion mixture and oil in large saucepan. Cook over medium-high heat, stirring frequently, until onion is fully softened and beginning to stick to saucepan, 5 to 7 minutes.

Step 2

While onion mixture cooks, process tomatoes and their juice in now-empty food processor until smooth, about 30 seconds. Add chile powder, cumin, turmeric, and fennel seeds to onion mixture and cook, stirring constantly, until fragrant, about 1 minute. Stir in chickpeas and their liquid and processed tomatoes and bring to boil. Adjust heat to maintain simmer, then cover and simmer for 15 minutes. While mixture cooks, chop reserved onion fine.

Step 3

Stir garam masala and salt into chickpea mixture and continue to cook, uncovered and stirring occasionally, until chickpeas are softened and sauce is thickened, 8 to 12 minutes longer. Season with salt to taste. Transfer to wide, shallow serving bowl. Sprinkle with chopped onion, remaining serranos, and cilantro leaves and serve, passing lime wedges separately.