In a large bowl whisk together all the ingredients for the marinade and then add in the diced chicken. Stir everything together until the chicken is thoroughly coated in the yogurt marinade. Let the chicken marinate for 30-60 minutes.

Heat a tablespoon of olive oil (or additional butter) in a large skillet. Add in the chicken leaving the excess marinade sticking to it. Sauté until it's cooked through and then remove it from the skillet and onto a plate.

Over medium heat, add the butter to the skillet. When the butter is melted add in the diced onion, garam masala, turmeric, cumin, salt and pepper. Sauté until the onion is tender, about 3 minutes, and then pour in the tomato sauce. Lower the heat and let the sauce simmer for 5-10 minutes so that it thicken slightly.

Slowly pour in the half and half or cream stirring the sauce as you pour. If using half and half, be sure the sauce isn't boiling, or you'll run the risk of it splitting.

Add the chicken back into the skillet and remove it from the heat. Off the heat, add in the Greek yogurt. Stir everything together until the chicken is coated and you can't see any white streaks from the yogurt. Garnish with chopped cilantro and serve over white or brown rice.