Preheat the oven to 230°C. Season the chicken inside and out with the salt and pepper and place two of the lemon halves inside the chicken cavity. In a small bowl, stir together the chives, thyme, oregano, parsley, tarragon, lemon zest and chopped garlic. Add the butter and stir until herb mixture is well tossed. Rub the chicken with the herbed butter. Place the chicken, breast side up, in a large sauté pan and add the remaining lemons halves, garlic heads and red onions to the pan and drizzle with the olive oil. Roast the chicken until the skin is well browned, about 60 minutes.