Heat the oven to 400°F. Line a rimmed baking sheet with parchment paper. Chop 2 slices of bacon into small pieces and cook them in a skillet over medium heat until crisp. Transfer to a paper towel-lined plate and let cool slightly.

In a large bowl, combine the ground turkey, egg, breadcrumbs, onion, milk, cooked bacon, ½ tablespoon Dijon mustard, ½ tablespoon maple syrup, salt, and pepper. Mix gently until just combined.

Shape the mixture into a compact loaf in the center of the prepared baking sheet. Lay the remaining 2 bacon slices across the top, tucking the ends underneath if needed.

In a bowl, toss the carrots, parsnips, and potatoes with the olive oil and dried thyme. Spread them around the meatloaf in a single layer, leaving a little space between the pieces.

Stir the remaining ½ tablespoon Dijon mustard and ½ tablespoon maple syrup together in a small bowl. Brush the mixture over the bacon-topped loaf.

Roast until the vegetables are tender and the center of the meatloaf reaches 165°F, about 40 to 50 minutes. If the bacon is browned before the meatloaf is cooked through, loosely cover the loaf with foil for the remaining cooking time.

Let the meatloaf rest for 5 minutes before slicing. Serve with the roasted root vegetables.