Remove and discard giblets and necks from hens. Rinse hens with cold water; pat dry. Split hens in half lengthwise. Remove skin; trim excess fat.
Place cilantro, lemongrass, coconut milk, 3 tablespoons honey, fish sauce, and remaining ingredients in a blender; process until smooth. Pour mixture into a large zip-top plastic bag. Add hen halves; seal and marinate in refrigerator 12 hours or overnight.
Preheat oven to 400°.
Remove hen halves from bag, reserving marinade. Place reserved marinade in a small saucepan. Bring to a boil; cook 1 minute, stirring frequently. Remove from heat.
Place hen halves, meaty sides up, on a broiler pan. Insert a meat thermometer into meaty part of a thigh, making sure not to touch bone. Bake at 400° for 30 minutes, basting frequently with the reserved marinade. Brush remaining 1 tablespoon honey over hens, and bake hens an additional 20 minutes or until thermometer registers 180°.