Mix white miso, sake, soy sauce, brown sugar and sesame oil together in an oven-safe glass or ceramic baking dish. Stir in chicken strips. Cover with clingfilm and let marinate in the fridge, at least 30 minutes.
Preheat oven to 190 C / Gas 5.
Bake in the preheated oven until marinade has thickened and chicken has cooked through, 30 to 35 minutes.