Preheat the oven to 350 degrees. Line a baking sheet with parchment paper. Using a bread knife, Slice the bread diagonally into 1-inch sections, making sure NOT to cut all the way through the bottom, so that the loaf stays intact. Slice the bread in the opposite direction on the diagonal, making sure to NOT cut all the way through. The bread should be sliced into 1-inch cubes, while still mostly in the bread loaf shape.
In a large bowl, mix together the grated cheese, sliced onions, and chopped parsley. Using fingers, stuff the cheese mixture around the cubes of bread. Drizzle melted butter over the top of the stuffed loaf.
Cover loaf with aluminum foil and bake in preheated oven for 20 minutes. Remove foil and continue baking for an additional 10 to 15 minutes until golden brown and the cheese is bubbling.