Raise the heat to medium and stir in the onion, garlic, ginger and serrano. Cook for about five minutes, stirring often. Stir in the garam masala (or tikka masala), coriander, turmeric, salt and cayenne (if using), and cook for two more minutes.
Cook the chana masala: In a Dutch oven or large saucepan, heat the oil over medium heat. When a drop of water sizzles upon hitting the pan, reduce the heat to medium-low and add the cumin seeds. Toast the seeds for a minute or two, stirring frequently, until the seeds are golden and fragrant. Watch carefully to avoid burning the seeds.
Cook the rice (if you want to serve the chana masala on rice): Bring a large pot of water to boil on the stove. Pour in the rice and give it a stir. Boil the rice for 30 minutes, then turn off the heat and drain the rice. Return the rice to the pot and cover the pot. Let the rice steam for 10 minutes. Remove the lid, fluff the rice with a fork and season with sea salt to taste.