Heat the oven to 400°F. Line a rimmed baking sheet with foil or parchment. In a large bowl, combine the ground turkey, egg, breadcrumbs, milk, diced onion, 1 tablespoon of the ketchup, Worcestershire sauce, salt, and black pepper. Mix just until combined.
Shape the turkey mixture into a compact loaf in the center of the prepared baking sheet. Lay the bacon slices across the top, tucking the ends underneath the loaf. Brush the remaining tablespoon of ketchup over the bacon.
In a separate bowl, toss the halved potatoes with olive oil, minced garlic, and dried rosemary. Arrange them around the meatloaf in a single layer, with their cut sides facing down where possible.
Roast until the potatoes are tender and the center of the meatloaf reaches 165°F, about 45 to 55 minutes. If the bacon needs more browning, broil briefly at the end, watching closely so it does not burn.
Let the meatloaf rest for 5 minutes before slicing. Serve with the garlic-roasted potatoes.