Place the oven to 200°C. Then start by flattening the chicken and cutting into strips. Lay out the flour, beaten egg and panko breadcrumbs in separate bowls. Place one chicken strip at a time in the flour then the eggs, wiping off the excess egg and then in the panko bread crumbs, crushing any ones that are a bit big. Place in the hot oven for about 20 minutes, or until completely cooked through, and start making the katsu sauce.
Slice the onion and garlic and dice the carrots. On a medium heat in a large sauté pan, add in nut oil and let this heat a minute. Add in the veg and let this cook for 15 minutes, until they are softened, you might want to use a lid as it will be quicker. Add in the curry powder and coat the veg. Add in the stock and let the veg sweat out and the sauce thicken. Do this for about 15 more minutes. Add on the remaining ingredients and stir. You can either blitz the sauce with a stick blender or pass the whole thing through a sieve.
Make the quick pickled radishes, this can be done whilst the sauce is cooking to save time. Wash the radishes and finely slice into rounds. Place in a small bowl with the vinegar and sugar and mix. Set aside to pickle whilst you wait for the sauce and chicken to finish cooking.
When everything is ready, stack up the chicken, place the sauce in a dipping bowl and scatter over the radishes.