In a 12-inch cast-iron skillet, stir together squash, apple, onion, 2 tablespoons oil, 1 tablespoon chopped rosemary, 1 teaspoon salt, and ½ teaspoon pepper; spread in a single layer.
Bake until squash is just tender, 15 to 20 minutes, stirring halfway through baking. Remove mixture from skillet, and let cool completely. Wipe skillet clean. Reduce oven temperature to 350°.
Place pork loin lengthwise on a cutting board, one short end closest to you. Holding your knife parallel to bottom of loin, make a lengthwise cut along bottom-third of one long side (image A). Open meat at incision as if you were opening a book (image B).
Again, holding your knife parallel to the cutting board with blade facing thicker side of loin, make another lengthwise cut along thicker side of loin, cutting to within ½ inch of other side. Again, open meat at incision as if you were opening a book (image C).
Using flat side of a meat mallet or a rolling pin, flatten any thicker portions of meat until you have an even thickness throughout. Do not flatten meat any thinner than ½ inch.
On a large piece of parchment paper, arrange bacon slices into strips, slightly overlapping. Place loin, cut side up, in center of bacon slices. Sprinkle remaining 1 tablespoon chopped rosemary, remaining 1 teaspoon salt, and remaining ½ teaspoon pepper onto pork. Spread squash mixture to within ½ inch of edges of loin.
Starting at one long side, roll up bacon, loin, and filling into a log (image D). Using kitchen twine, tie loin closed at 2-inch intervals (image E). Carefully transfer loin, seam side down, to same skillet; arrange rosemary sprigs around pork in skillet.
Bake until an instant-read thermometer inserted in center of pork registers 165°, about 1 hour. Increase oven temperature to broil. Broil until bacon is browned and crisp, 2 to 3 minutes. Remove loin from skillet, and let stand for 15 minutes.
Meanwhile, place skillet with drippings over medium heat. Whisk in flour. Cook, whisking constantly, for 2 minutes. Gradually whisk in broth and vinegar until smooth. Cook, whisking frequently, until sauce thickens, 12 to 15 minutes. Serve with pork loin. Garnish with rosemary, if desired.
Notes
Kitchen Tip: The squash filling can be made up to 2 days ahead and refrigerated. Peel the squash and apple if desired, but it’s not necessary.
Recipe by Paula Deen Magazine at https://pauladeenmagazine.com/bacon-wrapped-squash-apple-stuffed-pork/