Heat the oven to 425 degrees. Pat the chicken dry with paper towels and place it in a large roasting pan.
Zest one lemon and juice both lemons. In a small bowl, mix the lemon zest, lemon juice, olive oil, garlic, rosemary, thyme, salt, and pepper.
Rub half of the lemon-herb mixture all over the chicken, including under the skin where possible. Set the rest of the mixture aside.
In a large bowl, toss the carrots, parsnips, potatoes, and onion with the remaining lemon-herb mixture until evenly coated.
Arrange the vegetables around the chicken in the roasting pan.
Roast for 60 to 75 minutes, until the chicken reaches 165 degrees in the thickest part of the thigh and the vegetables are tender and browned at the edges.
Remove the pan from the oven and let the chicken rest for 10 minutes before carving. Serve the vegetables alongside the chicken slices.