If making your besciamella sauce fresh, allow it to cool down to room temperature in advance.
Cook the peas with olive oil, diced onion, salt, and black pepper.
Cook the bucatini pasta and drain.
Combine pasta, besciamella, peas, prosciutto, and Parmigiano cheese in a bowl.
Pour the mixture into a dish and let it cool.
Prepare a thin batter with flour and water, and breadcrumbs in separate bowls.
Cut the pasta mixture into pieces, double batter and bread each piece.
Fry the frittatine in hot oil until golden brown on all sides.
Serve warm and fresh.
