Roast the garam masala ingredients in a dry skillet over medium-low heat about 5 minutes or until the spices smell fragrant. Remove to a plate, cool, then powder in a coffee grinder.
Heat oil in a saucepan.
Add the onion and saute about 5 minutes over medium heat until the onions begin to caramelize slightly.
Add the garlic and stir for another minute until the garlic no longer smells raw.
Add the powdered spices- the turmeric, chili powder and all of the garam masala. Stir for another minute.
Add the tomatoes. Let them cook, stirring occasionally, until you see the oil beginning to separate, around five minutes.
Add the potatoes and chickpeas and stir thoroughly. Add salt to taste.
Let the mixture come to a boil, turn down the heat,and simmer for another 5 minutes. Mash some of the chickpeas and poatoes with the back of a ladle to thicken the sauce.
Add the coconut milk and turn off the heat. Stir the coconut milk in.
Add the cilantro and tomatoes for garnish. Spritz with some lemon. Serve hot!