In a large mixing bowl, combine boneless chicken breast chunks with Greek yogurt, minced garlic, grated ginger, garam masala, and lemon juice. Cover and marinate for at least 30 minutes.

Melt 2 tablespoons of butter in a skillet over medium heat. Add chopped onions and sauté for 5-7 minutes until golden brown.

Pour in the canned tomatoes and stir well. Let the mixture simmer for about 10 minutes until it thickens slightly.

Add marinated chicken pieces to the skillet and sear for 5-6 minutes until browned on all sides.

Reduce heat to low, add heavy cream, and simmer for an additional 5-7 minutes to thicken the sauce.

Garnish with chopped cilantro and serve over basmati rice or with naan.