Place canola oil in cast iron skillet about halfway up the side. Turn heat to medium.
Slice pork tenderloin into 3/4-inch medallions. You should get about 12. Rub both sides of each medallion with a thin layer of Dijon mustard.
Place panko bread crumbs in a medium bowl. Add Italian seasoning and salt and stir to combined. Dip one medallion into seasoned breadcrumbs and press into breadcrumbs. Flip and press other side into breadcrumbs. Repeat with the rest of the medallions.
Once the oil reaches 350 degrees, place 4 medallions in to cook for about 3 minutes or until the bottom gets golden brown. Flip and cook for another 2 minutes or until the other side gets golden brown. Remove from hot oil and let them dry on a wire rack. Sprinkle with salt. Repeat in two more batches. Serve immediately.