Heat the oil in a large pan or a pot over medium heat. Once the oil is hot, add the cumin seeds and let them toast for a few seconds until they start to sizzle and become fragrant.
Add the chopped onions, minced garlic cloves, and ginger, and cook for 3-4 minutes until the onions are lightly golden (see note 2).
Add all the spices: garam masala, turmeric, cayenne pepper, ground cumin, and ground coriander (see note 3). Cook until fragrant for around 30 seconds.
Add the chickpeas and cubed potatoes and toast for a couple of minutes. Then add the salt, crushed tomatoes, and a cup of water (or vegetable broth).
Bring the curry to a boil, then reduce the heat to medium-low to keep it gently simmering, and cook for around 15 minutes until the potatoes are tender (use a fork to check) and the curry thickens up.
Adjust salt to taste. If you like your curry spicy, now it’s the time to add extra chili.
Once the curry is ready, add the chopped cilantro.
Serve with brown or white basmati rice or naan bread, and garnish with extra cilantro, slices of red onions, and fresh chili.