First season the chicken breast fillet with salt and pepper and fry on both sides in a little heated olive oil.
Clean the peppers and cut into strips. Peel the onion and cut into rings. Fry the ingredients briefly with the meat, then deglaze the whole thing with the vegetable stock and add a sip of sherry. Cover everything and simmer on medium temperature for about 15 minutes. Test whether the meat is done and possibly add salt and pepper to the sauce (but this is usually not necessary).
This is best served with couscous or rice prepared according to the package instructions.