Heat the pellet grill or smoker to 225℉ with your choice of wood or pellets.
In a skillet over medium-low heat, sauté the sliced onions with about 1 tablespoon of butter until caramelized.
While the onions are cooking, trim the silver skin and excess fat from the pork loin. Then, butterfly the pork loin, cutting and unrolling, until it is about ½ to ¾" in thickness. After the loin is butterflied, it should be in a large rectangular shape that is even in thickness. *See notes for tips on butterflying.
Season the top side of the flattened pork loin with your all-purpose seasoning. Then, use a butter knife to spread the boursin cheese over the pork loin, leaving about 3" on one end without cheese or filling. Add the baby spinach in an even layer on top of the cheese. Top with the caramelized onions and the jarred roasted red peppers.
Starting at the end that has the cheese and filling ingredients, begin to roll the pork loin tightly, stuffing the ingredients inside as needed as you go. Continue rolling until you reach the end of the loin, then sprinkle the outside with all-purpose seasoning. Set aside while you make the bacon weave.
Lay out a sheet of aluminum foil or parchment paper on your work surface. Make a bacon weave – 1) Place 8-9 strips of bacon parallel to each other vertically on the foil, leaving a very small gap in between each strip. 2) Starting from the top, fold back every other strip of bacon about 1 inch. 3) Lay a strip of bacon horizontally across the unfolded strips. 4) Unfold the folded vertical strips back over the horizontal strip you just placed. 5) Then fold back the vertical strips that were not folded the first time. 6) Place another strip of bacon horizontally, alternating over-and-under pattern from the first horizontal strip. 7) Continue the process, folding back the alternating vertical strips and adding horizontal strips until the lattice is complete.
Carefully take the stuffed pork loin and place it in the middle of the bacon weave. Tuck the bacon up and around the pork loin. *TIP – Use the parchment or foil to help you roll the bacon around the stuffed pork. Then, use 3-4 pieces of butcher’s twine to tie up the bacon-wrapped pork.
Place the bacon-wrapped pork loin on the grill, and smoke for 1 hour at 225°F. After 1 hour, adjust the temperature of the grill to 275°F, and cook for an additional 1 hour. After the second hour, adjust the grill temperature to 325°F. Cook the pork until the internal temperature reaches 145°F. *Total cook time for us was 2 hours and 40 minutes, but times will vary. Always cook to the proper internal temperature.
Optional Vinaigrette Basting - In a small bowl, mix together 2 tablespoons mayonnaise and ⅓ cup Italian vinaigrette. When the pork loin reaches about 120℉ internal temperature, begin basting the loin with the Italian mixture. Baste about 2-3 times, allowing the mixture to set up in between each.
Once the pork internal temp reaches 145℉, remove the smoked pork loin from the grill and transfer to a cutting board to rest. Rest for about 15-20 minutes, then cut into slices that are about 1 – 1.5" thick and serve. *Be sure to remove the butcher's twine before serving.