In a medium bowl, combine the chicken pieces with Greek yogurt, lemon juice, turmeric, and half of the garam masala; allow to marinate for at least 15 minutes.
Heat the ghee in a large skillet over medium-high heat and sear the chicken until golden brown on all sides, then remove the chicken from the pan and set aside.
In the same skillet, sauté the finely diced yellow onion until translucent and soft, then stir in the minced garlic, grated ginger, and the remaining garam masala until fragrant.
Pour in the tomato puree and bring to a gentle simmer, allowing the sauce to cook for about 10 minutes until it begins to thicken.
Stir in the full-fat coconut milk to create a creamy consistency, then return the seared chicken to the skillet and simmer for another 5 minutes until the chicken is cooked through.
Season the sauce with sea salt and black pepper to taste, adjusting the spices if necessary.
Serve the chicken tikka masala over a bed of warm, fluffy basmati rice and garnish with freshly chopped cilantro before serving.