Rinse the scallop shells well under cold running water to remove any sand and grit. Set them aside to drain and dry.
Preheat your oven to 390°F.
Place the softened butter in a mixing bowl. Mince the onion and add it to the butter. Mince the parsley leaves and add them to the bowl. Using a fork, mix the butter, onions, and parsley to combine well.
Place a scallop inside of each shell half. Season each scallop with a nice pinch of salt. Top each with a spoonful of the onion and parsley butter.
Cover each scallop with breadcrumbs.
Place the filled scallop shelves on a sheet tray. Place the tray in the oven and bake for 8 minutes until the breadcrumbs are golden brown.