For the pork: Put an oven rack in the lower 1/3 of the oven. Preheat the oven to 350 degrees F.
In a small bowl, add the Dijon mustard, whole-grain mustard, honey, garlic, and rosemary and mix together until smooth. Arrange the pork in a 9 by 13-inch baking pan and spread the mustard mixture evenly over the pork. Starting on 1 side, lay a piece of bacon, lengthwise, on the pork. Lay another slice of bacon on the pork making sure to slightly overlap the first piece. Continue with the remaining bacon, until the pork is fully covered in bacon. Using 3 pieces of kitchen twine, secure the bacon in place. Roast for 1 hour. Cover the pan, loosely, with foil and roast for another 10 to 20 minutes until an instant-read thermometer inserted into the thickest part of the pork registers 160 degrees F. Remove the pan from the oven and transfer the roast to a cutting board. Cover the pan with foil and allow the pork to rest for 20 minutes. Remove the kitchen twine and slice the pork into 1/2-inch thick slices.
For the salad: In a small bowl, whisk together the lemon juice and oil until smooth. Season with salt and pepper, to taste.
Put the arugula on a large platter and drizzle with the dressing. Arrange the pork slices on top and serve.