Preheat oven to 450° F. Mix oil and butter together; gently lift the chicken skin from the breast and put oil and butter mixture between the flesh and skin. Season chicken with salt and pepper.
Place the chicken in roasting pan on a bed of vegetables. Place lemon inside the cavity of the chicken. Tie legs together with cotton string.
Roast chicken 20 minutes; reduce oven to 375° F. Roast chicken about 1 hour and 15 minutes
Lift chicken and tilt slightly, emptying juices from cavity into pan. Transfer to cutting board; cover with aluminum foil and wait 10 minutes before carving.