Cut the schnitzel into strips. Peel onion and chop finely. Drain the pineapple in a colander while collecting the juice.
Mix the meat, onion, 2-3 tablespoon pineapple juice and soy sauce. Marinate for approx. 20 to 30 minutes. In the meantime, clean the peppers and cut into fine strips.
Add the meat and pineapple pieces to the pepper strips in the wok and heat in it. Season the bell pepper pan with the remaining pineapple juice, salt and sambal oelek.