Cut one turnip into wedges and grate the other. Thinly slice the shiso leaves.

Season the chicken thigh with salt and pepper. In a microwave-safe bowl, mix mentsuyu and mirin, then microwave at 600W for 1 minute. Add the grated turnip and shiso leaves to the mixture.

Heat salad oil in a frying pan. Place the chicken skin-side down and add the turnip wedges. Cook until the turnips are tender, then remove them. Continue cooking the chicken on medium heat until browned, then flip and cover with a lid. Cook on low heat for 4 minutes.