Place the cabbage into a medium bowl. Add carrot and red onion. In a small bowl, whisk together the olive oil, vinegar, lemon juice, oregano and mustard. Toss the cabbage mixture with the dressing, and then stir in the feta cheese. Toss well, and season with salt and pepper.
Preheat your grill to medium heat. Butterfly the pork loin by taking a sharp knife and cutting it "almost" in half- just cut across to the other side so you can open it up and lay the opened up pork loin on the grill. Grill 5 to 7 minutes on each side. If you're using a meat thermometer, it should read 145 degrees F. when inserted into the middle of the loin. Add the buns to the grill toward the end of grilling, just to toast them a little. Remove the pork from the grill and let it sit on the cutting board for a few minutes, then slice it thinly.
Spread hummus on the bottom halves of each bun. Add pork slices on top of the hummus. Spoon some of the Greek cole slaw on top of the pork, and then top that with a few peperoncini slices. Add the top buns, and they're ready to serve!