Preheat oven to 425 degrees. For this recipe you can either use a small roasting pan or a 9 x 13 baking dish. I prefer to use a baking dish for easier clean up. If using a baking dish, take a long sheet of aluminum foil (approximately 2.5-3ft) and crinkle it into a snake. Place this in the baking dish to raise the chicken off the surface of the pan.
Remove and discard the chicken giblets. Rinse the chicken and pat it dry. Liberally season the inside of the chicken with salt and pepper. Place 2 lemon quarters and the head of garlic inside of the chicken.
Toss the remaining lemons and onion slices with olive oil, salt and pepper. Place in the bottom of a 9 x 13 baking dish or roasting pan. Put the chicken on the aluminum "snake" or on the roasting rack. Tuck the wing tips under the chicken breast and tie the drumsticks together with kitchen string.
Brush the chicken with olive oil and liberally season the chicken with salt, pepper, garlic powder, and paprika. Roast the chicken for 1 hour and 15 minutes. Halfway through if your onions are burning, add the chicken stock into the bottom of the pan and baste the chicken. Roast until the internal temperature of the breast reaches 165 degrees. Let the chicken rest for 15 minutes prior to carving.