Butterfly the chicken breasts if needed and pound them to an even thickness.
Season both sides with salt and pepper.
Coat each piece in flour, then dip into the beaten eggs.
Press both sides into the panko breadcrumbs until well coated.
Heat about 1 inch of oil in a skillet over medium heat.
Fry the chicken for 4–5 minutes per side until golden brown and cooked through.
Transfer to a paper towel-lined plate to drain.
Allow the chicken to rest for 5 minutes before slicing into strips.
Fill one side of the bento box with warm cooked rice and sprinkle with sesame seeds.
Arrange the sliced chicken katsu over the rice.
Add the shredded cabbage, steamed broccoli, tomatoes, cucumber, carrots, and pickled radish to the remaining compartments.
Drizzle the chicken with tonkatsu sauce or pack the sauce separately.
Serve warm or enjoy at room temperature.