Cut the chicken thigh into bite-sized pieces, season both sides with salt and pepper, and let sit for 2 minutes. Coat with potato starch.

Peel and julienne the carrot, thinly slice the onion, and cut the kaiware sprouts into halves, removing the roots.

In a bowl, mix the nanban sauce ingredients (vinegar, mentsuyu, yuzu kosho, and water) until well combined.

Heat sesame oil in a frying pan over medium heat. Add the chicken and cook until browned. Flip the chicken, then add the carrot and onion. Stir-fry until the vegetables are tender.