Combine onion, lemon juice, thyme, basil, and garlic in a roasting pan or large baking dish. Add the chicken and turn to coat on all sides.

Fill the cavity with the lemon halves, herbs, garlic, and as many of the onion slices as possible (the rest of the onion slices can just hang out in the bottom of the roasting pan). Tie the legs together with kitchen twine to keep everything from falling out. If you're not sure how to do this follow this video.  Rub the outside of the chicken with olive oil and season generously with salt and pepper.

If you have time refrigerate the chicken uncovered for a couple hours, or better yet, overnight to let the flavors soak in. If not, go ahead and heat the oven to 400°F and arrange the rack in the bottom third of the oven, leave the chicken out at room temperature while the oven heats.

Roast the chicken for about 1 hour 15 minutes, or until a thermometer inserted in the inner thigh reads 165°F. Baste the chicken occasionally during cooking; if the breast gets too brown before the chicken in completely cooked, cover it with a small piece of foil.

Transfer chicken to a cutting board and cover with foil. Let rest for at least 15 minutes before carving.