In a small mixing bowl, combine the yogurt, minced garlic, grated ginger, cumin powder, coriander powder, paprika, garam masala, turmeric, cayenne pepper (if using), lemon juice, salt, and pepper. Mix well until all the spices are fully incorporated into the yogurt.
Place the chicken breasts in a shallow dish or resealable plastic bag. Pour the yogurt marinade over the chicken, making sure all sides are coated. Cover and refrigerate for at least 1 hour or up to 8 hours.
Preheat your grill to medium-high heat (about 375-400°F).
Remove the chicken from the marinade and discard any excess marinade. Place the chicken on the grill, making sure to leave enough space between each piece. Grill for 6-7 minutes per side, or until the chicken is fully cooked (internal temperature of 165°F).
While the chicken is grilling, baste it with the leftover marinade using a clean basting brush.
Once the chicken is cooked, remove it from the grill and let it rest for a few minutes before serving.
Garnish with fresh cilantro (optional) and serve hot with your choice of sides, such as rice, naan bread, or a fresh salad.