Is the fish the one in saffron ? Given that saffron is such a delicate spice and sweet & sour peppers quite a strong flavour, I think I would simply add butter and black pepper to the spinach or it would overwhelm the fish. What carbohydrate are you serving up ? Plain rice would work well here btw.
lightly fry your fish, put to keep warm, in same pan add spinach, till it wilts, then a tub of Philly or similar, squeeze lemon, some crushed chillies, pour over fish. Tastes lovely, and looks almost cordon bleu.