Heat oven to 425°F.
Using a vegetable peeler, remove 6 strips of lemon zest, making sure to avoid the white pith. Thinly slice each strip crosswise.
In a small bowl, combine the butter, garlic, dijon mustard, lemon zest and ½ tsp. each of salt and pepper. Then set aside.
Remove skin from turkey breast. Rub butter mixture all over and place skin back on top.
Form into a log shape and wrap with butcher's twine to secure.
In another bowl, toss shallot with olive oil and ¼ tsp. each of salt and pepper. Arrange in the center of a large rimmed baking sheet or roasting pan.
Place turkey on top of the shallots. Roast for 45 minutes.
Meanwhile, chop carrots in half across the middle, then each half into 2 or 3 strips lengthwise. Repeat with parsnips.
Remove turkey from oven and transfer to cutting board.
Add carrots, potatoes and parsnips to baking sheet along with ½ teaspoon each of salt and pepper. Toss with shallots and pan gravy.
Place turkey back on top. Return to oven and and roast until turkey registers 165°F and vegetables are browned and tender, 30-45 minutes more.
Transfer to a clean cutting board and allow to rest for atleast 10 minutes before serving.
Remove vegetables and place in a dish.
Transfer pan juices to a pot (or put the roasting pan on the stovetop), add 1 cup of beef stock and 2 tablespoons of flour. Heat on medium-heat, whisking until gravy is free of lumps. Thicken with more flour or cornstarch as needed.