Peel and wash the plantains, then pat them dry.
Cut the plantains into 1.5-inch slices.
Heat the vegetable oil in a deep fryer or large saucepan to a medium-high temperature for deep frying.
Carefully add the plantain slices to the hot oil, ensuring they are fully submerged, and fry for about 7 minutes.
Remove the plantains and place them on a paper towel for around 5 minutes; they should not be overly dry.
Use a citrus squeezer or the back of a small bowl to press each plantain slice into a cup shape.
Place the formed plantain cups back into the fryer or saucepan with enough oil to submerge them, frying until they turn golden brown.
Boil smoked herring to reduce saltiness, then shred or chop finely for the stuffing.
Heat some olive oil and sauté the onion, green onions, and seasoning pepper in a frying pan. Add the shredded herring and black pepper, cooking until well combined and heated through.
Stuff the crispy plantain cups with the prepared herring mixture.
Serve immediately and enjoy!