01 - Preheat the oven to 400°F.
02 - Combine olive oil, chopped oregano, minced garlic, lemon zest, lemon juice, salt, and black pepper in a small bowl to create the marinade.
03 - Pat the chicken dry with paper towels. Thoroughly rub the marinade over the entire chicken, including under the skin and inside the cavity.
04 - Fill the chicken cavity with half of the onion wedges and several lemon slices.
05 - Place the remaining onion wedges and lemon slices in the roasting pan. Set the chicken breast-side up on top.
06 - Roast for 1 hour and 10 minutes, basting intermittently with pan juices, until the skin is golden and an internal thermometer reads 165°F in the thickest thigh portion.
07 - Allow the chicken to rest, loosely covered with foil, for 10 minutes before carving.
08 - Finish by garnishing with fresh oregano sprigs and serve alongside pan juices.