In a large mixing bowl, combine the Greek yogurt, garlic, ginger, garam masala, turmeric, cayenne pepper, salt, and black pepper. Stir until well combined. Add the chicken breasts or thighs, ensuring they are fully coated. Cover and let marinate for at least 30 minutes, or preferably overnight in the refrigerator for deeper flavor.
Preheat your oven to 400°F (200°C). This ensures that the chicken cooks evenly and becomes beautifully golden.
In an oven-safe baking dish, melt the salted butter over medium heat on the stove. Add the chopped onion and sauté until translucent and fragrant, about 5 minutes. Stir in the tomato paste and cook for another 2 minutes before adding the coconut milk. Mix well to create a smooth sauce.
Place the marinated chicken into the baking dish, making sure it is submerged in the coconut sauce. This not only flavors the chicken but ensures it remains moist during baking.
Sprinkle sesame seeds over the chicken and sauce. Bake in the preheated oven for 30-35 minutes, or until the chicken is cooked through and reaches an internal temperature of 165°F (74°C). For an extra touch, switch the oven to broil for the last 5 minutes to achieve that perfect golden crust.
Once out of the oven, let the chicken rest for a few minutes. Garnish with fresh cilantro or mint, jalapeño slices, and a squeeze of lemon juice. Serve with steamed rice and naan, along with pickled ginger and sliced cucumbers on the side for a refreshing crunch.