Heat the oven to 400°F. Line a rimmed baking sheet with parchment paper or lightly grease it.
In a large bowl, mix the ground turkey, grated apple, chopped dried cranberries, panko, egg, milk, sage, salt, and pepper. Stir just until combined so the meatloaf stays tender.
Shape the mixture into a compact loaf on one side of the baking sheet.
Toss the Brussels sprouts with the olive oil, then arrange them cut side down around the meatloaf. Leave a little space between the sprouts so they roast rather than steam.
Bake for 25 minutes. Spoon the cranberry sauce over the top of the meatloaf, then return the pan to the oven. Bake for about 15 more minutes, until the meatloaf reaches 165°F in the center and the sprouts are browned and tender.
Let the meatloaf rest for 5 minutes before slicing. Serve with the roasted Brussels sprouts.