Heat the oven to 375°F. Line a rimmed baking sheet with parchment paper.
In a large bowl, combine the ground turkey, egg, breadcrumbs, onion, Dijon mustard, garlic, salt, and black pepper. Mix gently until just combined. Avoid overmixing, which can make the meatloaf dense.
In a small bowl, stir together the crumbled bacon and blue cheese. Set the filling aside.
Place the turkey mixture on the prepared baking sheet and shape it into a rectangle about 8 by 10 inches. Spoon the bacon and blue cheese mixture down the center, leaving a border around the edges. Fold the turkey mixture over the filling and pinch the seams closed. Shape it into a compact loaf with the seam underneath.
Bake until the center of the meatloaf reaches 165°F, about 40 to 50 minutes. Let it rest for 10 minutes before slicing so the filling stays in place.
While the meatloaf bakes, whisk the mayonnaise, apple cider vinegar, and honey in a medium bowl. Add the apple matchsticks and sliced cabbage, then toss to coat. Chill the slaw until ready to serve.
Slice the meatloaf carefully and serve with the apple slaw alongside.