Remove and discard the tough outer skin from the lemon grass stalks and roughly chop. Put lemongrass, chilies, garlic, green onion, fresh cilantro, cumin, pepper, turmeric, ground coriander, lime zest, lime juice, ginger, fish sauce and coconut milk in a food processor or blender; pulse until smooth.
In a bowl, toss chicken with lemongrass mixture. Cover and refrigerate for 1 hour.
Grill over medium hot coals, until the chicken is opaque with no trace of pink, approximately 3 minutes per side. Sprinkle with salt and pepper. Serve hot.