Lay the chicken breasts on a large sheet of greaseproof paper, cover with another sheet and bash flat with a rolling pin, until about 1cm thick.
Tip the flour onto a plate and season with sea salt and black pepper. Beat the egg in a shallow dish with a pinch of salt, then tip the panko onto a plate. Coat the chicken breasts in the flour, then in the beaten egg, shaking off any excess, and press into the breadcrumbs to coat. Set aside while you make the pickle.
Peel the carrot and cut into matchsticks. Halve the cucumber, deseed and thinly slice. Trim and slice the radishes. Combine in a bowl with the rice vinegar, sugar, sesame seeds and a pinch of salt.
Strain the curry sauce into a pan and bring to a simmer. Add the chicken stock, soy sauce and rice vinegar. Reduce the heat and simmer for 3 minutes. Trim and slice the spring onions and set aside.
Heat the sunflower oil in a large frying pan until simmering hot. Carefully add the coated chicken breasts and cook for 2 to 3 minutes on one side, until golden and crisp. Turn and cook the other side until the chicken is cooked through. Remove from the pan and transfer to kitchen paper to drain.
Slice each chicken breast into strips and serve with the sauce, and the sliced spring onions and pickle on top. Delicious with a mound of sticky rice.