Place the soy sauce, sesame oil and 5-spice powder into a bowl and mix. Add the chicken and toss together to coat in the marinade. Cover and set aside for 1 hour, stirring occasionally.
Thread the chicken, zigzag fashion, on to 10 soaked bamboo skewers (soaking them in warm water for 30 minutes will prevent the sticks burning while cooking), and place the chicken under a hot grill for 8–10 minutes, turning once, until golden and cooked through.
Meanwhile, put all the sauce ingredients in a small pan and heat, stirring, until warm and well mixed. Transfer to a small serving bowl.
Place the bowl of sauce on a serving plate with the cucumber on one side and the hot chicken skewers around it.