Zest the yellow rind of the lemon. Cut the lemon in half and juice half of the lemon into a small bowl. Add the rind, olive oil, softened butter, garlic, salt and pepper. Stir well (the mixture should be fairly thick).
Gently lift the skin from the chicken breasts and place about 1 tablespoon of the butter mixture under the skin. Massage it evenly across the breasts.
Cover the skin of the chicken with the remaining butter mixture. Refrigerate for 30-45 minutes.
Preheat oven to 425 degrees. Slice the remaining lemon half and place it inside the chicken along with 1/2 an onion. Tie the legs together. Place the chicken in a shallow pan breast side up and place in oven.
Turn oven down to 375 degrees F and bake for 1 1/4 hours or until the inner thigh reaches 165 degrees F.
(Nutrition information provided is an estimate and will vary based on cooking methods and brands of ingredients used.)