Meanwhile, spread the rest of chopped onions, carrots, and celery on the roasting pan. Transfer turkey on top of vegetables on the roasting pan. Stuff the turkey with 1/2 chopped onion, 1 chopped celery, 2 sage leaves, 2 sprigs thyme, 2 sprigs parsley, 2 smashed garlic cloves. 3 slices of lemon, 1/4 tsp salt and freshly ground pepper. Insert 2 fingers under the skin on each breast section while pushing in gently. This will create a pocket. Inside this pocket insert 1 tbsp butter, 1/4 tsp dried Italian seasoning, and 1 slice of lemon. Push it in gently until it reaches the center of the breast. Pull breast skin back down. Repeat this process for the other side of the breast. Brush olive oil all over the turkey. Season it generously with salt and freshly ground pepper. Sprinkle dried Italian seasoning all over the turkey. Tuck wing tips under the shoulder of the turkey. Truss the turkey by tying the end of the drumsticks on top of each other with a cooking twine. Tie with a knot twice. Cut off extra twine, leaving 1/2 inch.