Gather all your marinade ingredients. In a bowl that will hold the chicken, add all the marinade ingredients except the chicken.
Cut the chicken into bite-sized pieces. I prefer roughly 1 1/2 by 1 1/2 cubes. Combine the spices and lemon juice, then thoroughly coat the chicken. Set aside to marinate.
Masala (Sauce)
Heat the coconut oil in a wok or dutch oven over medium-high heat. Turn the heat down to medium and add the onion and salt. Cook for 8 to 12 minutes until the edges turn golden brown.
Stir in the curry leaves (if using), the minced green chili, and the ginger garlic paste. Sauté for 2 minutes or until the ginger and garlic no longer smell raw.
Add the Kerala garam masala (OR the 3-spice combination in Notes), turmeric, and red chili powder. Sauté for 1 minute, adding a tablespoon of water if the masala is sticking to the bottom of the pan.
Stir in the tomatoes and cook for 5 to 6 minutes until the sauce darkens and thickens. (Fresh tomatoes will take longer to break down.) The oil will begin to separate along the edges. Turn the heat to medium-high and add the chicken (and the lime zest if using instead of curry leaves) and cook for 3 minutes.
Stir in the coconut milk and bring to a simmer. Cover the pan and turn the heat down to low, or whatever temperature keeps the stew cooking at a very low simmer. Allow to cook for about 8 to 10 minutes or until the chicken is cooked through and tender.
If using chicken breasts begin checking for doneness in 5 minutes. Stir in the final garam masala and kasoori methi if using.
Serve with rice and your favorite flatbread. This curry freezes very well.
Notes
If using chicken breasts: Start checking at the 5-minute mark for doneness so as not to dry out the meat.
Curry leaves add herbaceous, anise, and citrus notes to a dish. If you can’t find them, you can add 1/2 teaspoon of lime rind. The result won't be the same but the zest will add some of the citrus notes you get with the real thing. Try to find unwaxed fruit or scrub well.
Green and ground red chili: This amount of chili will give you a low hum of heat. Feel free to add more or less to taste. The same goes for the ground red chil.