Combine Japanese mayonnaise, margarine and mustard in a small mixing bowl and set aside.
Place the pork on a chopping board and tenderize with a meat mallet.
Shape the meat to size the same size of the bread that will be used.
Apply pinch of salt and pepper over the pork.
Combine egg, water and Japanese mayonnaise in a medium mixing bowl and whisk.
Add flour and mix them all together to make batter.
Dip the shaped meat carefully to keep the shape with your hands.
Coat the meat well with the batter.
Scatter the Panko breadcrumbs on shallow container.
Place the pork coated with batter on the panko breadcrumbs.
Coat the pork well with panko breadcrumbs.
Heat deep frying oil to 170 °C (338°F) in a fryer or frying pan. *5
Once the oil temperature reached desirable temperature, deep fry the pork for about 8-10 minutes. *6
When it is cooked remove from the oil onto a tray lined with kitchen paper and set aside.
Combine tonkatsu sauce and tomato sauce. Set aside.
Place two slices of bread on a chopping board.
Spread the margarine, mayonnaise and mustard mixture thinly and evenly.
Place 1/2 cup of shredded cabbage on to a bread.
Drizzle the tonkatsu sauce generously over one side of the Katsu.
Place the tonkatsu sauce drizzled side down onto the cabbage.
Drizzle more tonkatsu sauce mixture generously over the another side of the pork.
Place a piece of bread on top of the fried pork to sandwich.
Put a flat plate over the bread and place weight on for 5 minutes.
After 5 minutes, remove the plate and weight and cut it in half to serve.