Begin by preparing the chicken. Place the chicken breasts between two sheets of plastic wrap and pound them to an even thickness, about 1/2 inch thick. Season both sides with salt and pepper.
Set up a breading station: Place the flour in one shallow dish, beat the eggs in a second dish, and put the panko breadcrumbs in a third dish.
Dredge each chicken breast in flour, shaking off the excess. Dip it into the beaten eggs, then coat it thoroughly with panko breadcrumbs, pressing gently to adhere.
In a large skillet, heat about 1/4 inch of vegetable oil over medium-high heat. Once hot, carefully add the breaded chicken breasts. Fry for about 4-5 minutes on each side, or until golden brown and cooked through. Remove from the skillet and drain on paper towels.
While the chicken is frying, prepare the bowls. Divide the cooked rice among four bowls. Top each bowl with shredded cabbage and sliced green onions.
Slice the fried chicken into strips and place on top of the rice and vegetables. Drizzle with tonkatsu sauce and sprinkle with sesame seeds if desired.
Serve immediately and enjoy your crispy chicken katsu bowls!