Trim and clean the fish, and salt lightly. Set aside.
Pour the olive oil into a large flameproof casserole (preferably earthenware, although this is not essential). Heat, then add the onions and brown. Add the garlic, parsley, chilies and bay leaves, then add the tomatoes and vinegar. Stew for a while, stirring occasionally. Do not allow the ingredients to burn and stick. Pour over a little water and add the peppercorns, piri piri sauce, salt, and nutmeg, to taste. Bring to the boil.
Meanwhile, rinse the fish to remove the excess salt but do not skin or bone. Cut fish into slices (except the sardines, which should be left whole, but decapitated). Add the fish to the stew in layers, with the tougher fish at the bottom. Layer the strips of green pepper between each layer of fish. Put the sardines on the top so that they don't break up.
Spread the butter over the bread. Place the bread over the top of the sardines, buttered side down. Cover and cook over a low heat, shaking the casserole from time to time to prevent sticking; do not uncover. When the contents begin to boil, and the liquid has soaked and covered the bread completely, the dish is ready to serve. Place a slice of bread and a sardine on each plate and ladle over the rest of the stew.