Prepare the tonkatsu: Heat oil in a large skillet over medium-high heat. Dredge the pork cutlets in flour, then egg, and finally in panko breadcrumbs. Fry the pork until golden brown and crispy, about 3-4 minutes per side. Drain on a paper towel-lined plate and set aside.

Make the tamago (Japanese-style egg salad): In a medium bowl, combine the chopped hard-boiled eggs, 2 tablespoons of Japanese mayonnaise, and a pinch of salt and pepper. Mix well until the eggs are evenly coated.

Assemble the Mixed Sando: Spread a thin layer of Japanese mayonnaise on one side of each slice of bread.

On the mayonnaise-coated side, place a layer of tonkatsu, followed by a spoonful of the tamago egg salad, a few slices of cucumber, a small handful of shredded lettuce, and a couple of cherry tomato halves.

Gently close the sandwich with the remaining bread slices, pressing down lightly to secure the fillings.

Using a sharp knife, slice each sandwich diagonally or in half to reveal the layered interior.

Serve the Mixed Sando immediately, drizzling Tonkatsu sauce over the top or on the side for dipping.