Pork Katsu Sandwich

Name: Pork Katsu Sandwich
Ingredients: 12 oz. boneless pork loin, fat trimmed 1/4-thick; 1/3 cup shio koji seasoning; 2 tsp. kosher salt; 1/2 small head of green cabbage, core removed, very thinly sliced (about 3 cups); 2 Meyer lemons or regular lemons; Kosher salt; 2 large eggs, beaten to blend; 3 cups panko (Japanese breadcrumbs); 1 cup all-purpose flour; Vegetable oil (for frying; about 6 cups); Tonkatsu sauce, preferably Bull-Dog, and Dijon mustard (for serving); 8 (1/2-thick) slices milk bread, crusts removed