In a large bowl, combine the Greek yogurt, olive oil, minced garlic, grated ginger, garam masala, ground cumin, ground coriander, paprika, ground turmeric, cayenne pepper, salt, black pepper, and lemon juice. Whisk until well mixed to create the tandoori marinade.
Place the chicken breasts in the marinade and ensure they are thoroughly coated. Cover the bowl with plastic wrap and refrigerate for at least 2 hours, or overnight for deeper flavor penetration.
Preheat your grill or a grill pan over medium-high heat. If using an oven, preheat to 375°F (190°C).
Remove the chicken from the marinade, shaking off excess. Place the chicken on the grill or a baking sheet lined with parchment paper if using an oven.
Grill the chicken for about 6-7 minutes on each side or until the internal temperature reaches 165°F (74°C). If baking, cook for 20-25 minutes or until the chicken is thoroughly cooked and the juices run clear.
Once done, remove the chicken from the grill or oven and let it rest for a few minutes before slicing.
Serve hot, garnished with fresh cilantro if desired.