This sandwich is about half the size of the original, because it uses a pork tenderloin rather than the larger cut of pork loin. It is pan-fried instead of deep-fried, but offers the same whole-hearted flavor that has made this sandwich an Iowan classic.
Weigh or lightly spoon flour into a dry measuring cup; level with a knife. Place flour in a shallow bowl. Combine 1 tablespoon water and egg in a second shallow bowl, stirring with a whisk. Combine breadcrumbs and parsley in a third shallow bowl.
Cut pork crosswise into 4 pieces. Place pieces between 2 sheets of heavy-duty plastic wrap; pound to 1/4-inch thickness using a meat mallet or small heavy skillet. Sprinkle both sides of pork evenly with salt.
Heat a large nonstick skillet over medium-high heat. Add 2 tablespoons oil to pan; swirl to coat. Dredge half of pork in flour; dip in egg mixture, and dredge in breadcrumb mixture. Cook pork in hot oil 3 minutes on each side or until tender. Repeat procedure with remaining oil and pork.
Place 1 lettuce leaf on each bun bottom. Top each with 1 piece of pork and 2 pickle slices; add ranch dressing, mustard, ketchup, or chopped onions, if desired. Cover with bun top.