Preheat your oven to 425ºF. Place the top rack in the center of the oven.
Rinse your chicken with cold water inside and out and dry well with paper towels.
Liberally salt and pepper the inside of the chicken.
Shove the quartered onion, lemon, if you are using and the fresh herbs inside the carcass of the chicken.
Brush the outside of the chicken with olive oil (or melted butter or ghee). Rub it all over evenly.
Sprinkle the chicken generously with sea salt and black pepper, or any other seasonings you want to include.
Using some kitchen twine, tie up the chicken legs, tuck the wing tips under the body, if you can. This makes for more uniform cooking.
Add any vegetables to the roasting pan, toss with a drizzle of olive oil and a little salt and pepper.
Place the chicken breast side up, on top of the vegetables.
Roast the chicken for approximately 1 1/2 hours (more like 1 hour 15 minutes if it's closer to 4lbs), or until the juices run clear when you cut between a leg and thigh. If you see a rosy pink color, it will need more time. Continue to roast, checking every 5 minutes, until juices run clear. To test with a instant read thermometer, insert into the inner thigh (but not touching the bone) it should register 165°F.
Let chicken rest, at least 15 minutes before carving. Transfer chicken to a platter and serve with the vegetables.Garnish with fresh herbs.
Notes
For low FODMAP leave out the onion, swap in celery or fennel