Prepare chicken by cutting into bite sized chunks. In mixing bowl whisk together coconut milk, Greek yogurt, cream, tomato paste, garlic, ginger and all the spices. Make sure it is mixed very well and there are no chunks.
Lightly spray the inside of your slow cooker with cooking spray. Add the diced onion to the bottom of the slow cooker and top with cut up chicken. Pour the tomato/coconut milk over the chicken to make sure the chicken is completely covered. Top the liquid with butter. Top slow cooker with lid and cook on high for 4 hours or on low for 6 to 8 hours. I stir mine ½ way through cooking time if I remember.
Season with salt and pepper, serve over rice topped with chopped cilantro.
Great side to go with this is Naan. There is a great recipe over at Gimme Some Oven
Recipe from [Easy Slow Cooker Chickenhttp://www.halfbakedharvest.com/easy-healthier-crockpot-butter-chicken/]