In a medium bowl, whisk together the Greek yogurt, lemon juice, half of the garam masala, turmeric, and cumin.
Cut the chicken breast into bite-sized pieces and toss in the yogurt marinade, letting it sit for at least 15 minutes.
Melt the ghee in a large skillet over medium heat and sauté the diced yellow onion until softened and translucent.
Add the minced garlic and grated ginger to the skillet, stirring for 60 seconds until the aromatics are fragrant.
Add the marinated chicken to the skillet and cook for 5 minutes, allowing the exterior to brown slightly.
Stir in the tomato puree and the remaining garam masala, then reduce heat to low, cover, and simmer for 10 minutes.
Uncover and stir in the full-fat coconut milk, sea salt, and black pepper, simmering for an additional 2 minutes to thicken.
Serve the warm butter chicken over the cooked basmati rice and garnish with freshly chopped cilantro.