In a small bowl, toss the cubed chicken breast with Greek yogurt, turmeric, cumin, sea salt, black pepper, and half of the garam masala; let marinate for 15 minutes.
Heat the olive oil in a large skillet over medium heat and sauté the finely diced onion until it becomes translucent and soft.
Add the minced garlic and grated ginger to the skillet, stirring constantly for 1 minute until the mixture is fragrant.
Increase the heat slightly, add the marinated chicken to the pan, and cook until the pieces are lightly browned on all sides.
Pour in the tomato puree and the remaining garam masala, stirring to combine, then reduce heat and simmer for 10 minutes.
Stir in the full-fat coconut milk to create a rich, creamy sauce and allow it to heat through for an additional 2 minutes.
Serve the warm chicken tikka masala over the cooked basmati rice and garnish with fresh chopped cilantro.