Pat the chicken breasts with paper towel. On a cutting board, hold down the meat with your palm. Using a sharp knife, slice the chicken in half horizontally with your other hand. Repeat with the rest of the chicken.
Use a meat mallet or the back of the knife to pound on the entire meat surface. This will tenderize the chicken. Season each chicken cutlet with salt and pepper.
Prepare three shallow bowls, or wide rimmed plates. To one, add the flour. To the second one, lightly beat 2 large eggs, and to the last one, add your panko breadcrumbs. Dredge a chicken cutlet lightly with flour.
Next, dip the chicken in the beaten eggs. Make sure to let the excess egg drip back to the bowl as needed.
Lastly, coat the chicken in the panko. Press the panko to the chicken to make sure they stick. Repeat the process with the remaining cutlets, and arrange them in a baking sheet or large tray.
Heat about ¼ cup of olive oil in a large skillet or frying pan. Once it shimmers, add 2-3 pieces of breaded chicken, making sure not to over crowd your pan. Fry for 3-5 minutes each side, or until nicely golden. Note that the temperature of the chicken should be 165 F or 74 C on an instant-read thermometer.
Let chicken sit for 5 minutes, then slice into strips. Serve with tonkatsu sauce, rice and cabbage salad. Garnish with green onions.