Prepare the chicken breasts. Use a sharp knife to cut off the tenderloin and the narrow end of the chicken. Then slice the thicker pieces of the breast horizontally through the middle.
Place a piece of parchment paper over the chicken pieces and use a meat mallet to flatten them slightly. This will give you a larger, thinner surface area for quicker and more even cooking.
Season the chicken pieces with salt, pepper, onion and garlic powder on both sides.
Set up a breeding station with three shallow bowls. Place the flour in one bowl, the beaten eggs in another, and the breadcrumbs in the third bowl.
Dredge each chicken breast in the flour, shaking off any excess. Then dip it into the beaten eggs, allowing any excess to drip off. Finally, coat the chicken in the breadcrumbs, pressing lightly to ensure they adhere well.
Heat vegetable oil in a large frying pan or skillet over medium-high heat (7 on induction). You want enough oil to cover the bottom of the pan but it should be a thin layer as the chicken pieces are quite thin.
Once the oil is hot, carefully add the breaded chicken breasts to the pan. Cook for about 4-5 minutes per side, or until golden brown and cooked through. The internal temperature of the chicken should reach 165°F (74°C).
Remove the cooked chicken from the pan and place it on a paper towel-lined plate to drain any excess oil. Allow it to rest for a few minutes before slicing or serving.
While the chicken is cooking or ahead of time, prepare other components of the burger.
Make Katsu sauce. Combine all listed ingredients in a bowl, whisk through and set aside.
Thinly shred the cabbage, cutting the longer pieces in half. Place in a bowl and drizzle with about a tablespoon of vinegar, season with a pinch of salt and add a pinch of sugar and 2 tablespoons of mayonnaise. This coleslaw only needs to be lightly dressed because we will have additional creamy sauce in the burger.
Toast the burger buns. You can lightly toast them in a toaster or butter the insides and toast them in a skillet for extra flavor and texture.
Once the buns are toasted, it's time to assemble your katsu chicken burger. Take the bottom half of a bun and spread a generous amount of the curry-spiced sauce on it.
The next order of things is up to you. You can place a piece of crispy katsu chicken on top of the sauce followed by coleslaw or you can spoon a generous amount of coleslaw first and put the chicken on top. The coleslaw will provide a refreshing contrast to the crispy chicken and add some texture to your burger.
Top with fresh fried shallots and fresh cilantro leaves. You can add additional toppings such as lettuce leaves, tomato slices or even extra pickles.
Finally, spread more sauce on the top half of the toasted bun and place it on top. You can drizzle more mayo if you like.
Serve your katsu chicken burger immediately while the chicken is still warm and crispy. You can enjoy it as is or pair it with a side of fries or a green salad for a satisfying meal.