Preheat the oven to 450°F and line a roasting pan, baking sheet, or baking dish with parchment paper or foil to facilitate cleanup.
Place the prepared chicken on a clean work surface. Combine the softened butter, minced garlic, chopped rosemary, and lemon zest in a small bowl, mixing thoroughly to create a herbaceous butter.
Evenly distribute the butter mixture over the chicken, ensuring full coverage for enhanced flavor. Generously season the chicken’s exterior with salt, freshly cracked black pepper, and paprika. Apply additional salt and pepper inside the cavity.
Insert the rosemary sprigs, parsley, and lemon halves into the chicken’s cavity. Secure the bird by tucking the wing tips beneath its back and tying the legs together with kitchen twine.
Combine the carrots, celery, parsnips, potatoes, fennel, and onion in a mixing bowl. Drizzle the vegetables with olive oil, season with salt, pepper, and Herbes de Provence, and toss to coat evenly. Spread the vegetables on the prepared roasting pan, arranging the halved garlic head cut-side down among them.
Position the seasoned chicken breast-side up on top of the vegetable bed. Insert a digital thermometer into the thickest portion of the chicken breast. Reduce the oven temperature to 400°F and roast until the internal temperature reaches 165°F, which typically takes 1 hour and 20 minutes to 1 hour and 30 minutes.
Remove the chicken from the oven and allow it to rest for approximately 15 minutes. Carve the bird into portions and serve with the roasted vegetables. For added indulgence, pair the meal with warm crusty bread.