Preheat your oven to 425°F (220°C).
Pat the chicken dry with paper towels.
Rub the chicken all over with olive oil.
Season generously with salt and pepper.
Stuff the cavity with lemon halves, garlic, and herbs.
Place the chicken breast-side up on a roasting pan.
Quarter the onion and place around the chicken.
Roast in the preheated oven for about 1 hour and 15 minutes.
Use a meat thermometer to check the internal temperature (165°F or 75°C).
Let the chicken rest for 10-15 minutes before carving.