Mix the oil with the salt and pepper, then brush some of it over the top of the turkey. Put the fennel, onion, lemon slices, and halved garlic bulb into a baking pan large enough to fit the turkey, too. There’s no need for a rack, though, since the vegetables will be performing that function. Drizzle the rest of the oil over the vegetables, then arrange the turkey on top, oiled skin side up.
As to what you’ll be doing with the vegetables once the turkey is done, the root vegetables can be served as a side dish, while the baked garlic is more of a lagniappe. McGlinn describes it as “super soft and delicate flavored,” and notes that “you can squeeze it out and use it for other dishes like your mashed potatoes, or spread it on crostinis for an appetizer.”