Rinse the chicken in side and out under cold water. Pat dry and let sit at room temperature for 30 to 60 minutes.
Slice the lemon paper thin and remove the seeds. Lift the skin off the breast of the chicken and place 3 lemon slices and 3 sage leaves in between the skin and the meat of each breast. Place onion, garlic, thyme and the remaining lemon in the cavity of the chicken. Rub the entire chicken liberally with olive oil. Salt the outside and the cavity of the chicken.
Place in a 425 degree F oven on a roasting rack, breast-side-up. Place a meat thermometer in the thigh and cook until the chicken reaches 160 degrees F. This will take about 10-15 minutes per pound. Remove the chicken from the oven and let it rest for 10 minutes.
Combine all ingredients and let sit for 2 hours or more for best results.