Prepare 3 boiled eggs and remove the shell. Cut each egg in half and pop out the yolks into a separate container. Chop the remaining egg whites to make mashing it all together easier.

Pound the boneless pork loin under a plastic wrap using a meat tenderizer or rolling pin until it becomes a little less than a centimeter thin. Season with salt and pepper.

In three separate plates or bowls, place the flour and panko and beat the egg. Begin dredging by first coating the pork loin with flour and dust off any excess. Transfer the pork loin to the egg and fully coat it to ensure the panko will stick completely. Finally coat the pork loin with panko and lightly press in to make sure the panko pieces stick.

In a deep pan or saucepan, heat about an inch to an inch and a half deep of vegetable oil or any other neutral oil. When the oil has reached 340-355°F/170-180°C carefully place the breaded tonkatsu into the oil. Let fry for one minute then flip and let the other side fry for one minute as well or until golden brown. Remove from oil and place on a frying rack or cooling rack to allow excess oil to drip.

Prepare the vegetables. Cut two slices of tomato, both about 1cm in thickness, and cut both in half, creating four half moon shapes. Cut off both ends of a cucumber and cut to match the length of your bread slices. Cut a long slice of cucumber also about 1cm thick. You should have a long and flat rectangle of cucumber.

Prepare two slices of bread by spreading a thin layer of Japanese mayonnaise on both slices. Lay the halfmoon tomato slices on the opposite sides of the bread with the curved sides facing each other, fitting in like a puzzle. The tomatoes should occupy the two outer thirds of the slice of bread, leaving the middle third for the cucumber. Place the cucumber rectangle in the middle and place the other slice of bread on top, completing the tomato cucumber sandwich. Wrap with plastic wrap or parchment paper and set aside for now.

For the next sandwich, spread roasted sesame dressing on two slices of bread. On one slice lay down the slice of cheddar cheese, followed by the slices of ham. Place the leaf of lettuce on top of the ham, fold as needed to fit the slice of bread. Cover with the other slice of bread and the ham and cheese sandwich is done. Wrap with plastic wrap or parchment paper and set aside for now.

For the egg salad sandwich, simply prepare two slices of bread. On one slice, spread a generous layer of the egg salad mixture that was prepared earlier. The egg salad should be about 1.5cm or half an inch thick. Cover with the other slice of bread, completing the egg salad sandwich. Wrap with plastic wrap or parchment paper and set aside for now.

For the last sandwich, spread tonkatsu sauce evenly on two slices of bread. Place the tonkatsu onto the bread, and finish the katsu sando by placing the other slice of bread on top. Wrap with plastic wrap or parchment paper and set aside for now.

After the sandwiches have rested for about 10 minutes, cut them in half. Make sure to check the orientation of the cut for the tomato cucumber sandwich so the pattern of the colors is visible. Place the sandwich halves into a bento and the sandwich bento is done! 完成です！