Heat grill on high. Cut the top off the garlic bulb (not the root end). Place the garlic on a piece of aluminum foil, drizzle with olive oil, and close foil around garlic to seal. Place on grill. Close cover of grill and cook for about 20-25 minutes. Remove from grill and allow to cool until able to handle. Squeeze garlic cloves out of bulb into bowl of a processor.
To garlic, add all ingredients for herb and lemon sauce. Process until smooth and reserve.
Place rosemary and thyme under chicken skin. Season chicken with salt and pepper. Place chicken, skin side down on grill. Grill for 5 minutes then turn. Close grill, reduce heat to medium, and continue to grill for 25-30 minutes or until an instant read thermometer inserted into the thickest part of the thigh reads 170 degrees F.
Remove from grill and place chicken on a cutting board. Allow chicken to rest for 15 minutes. Place on serving dish and drizzle generously with herb and lemon sauce.
Garnish with fresh lemon slices and parsley sprigs. Serve.