TO PREPARE AND SERVE
Preheat the oven to 350° or bring a gas or charcoal grill to medium-hot heat. Melt the butter in a frying pan and add the onion. Sauté until onion is soft. Add parsley, garlic and breadcrumbs and cook about 1 minute. Remove from heat and cool. Add cheese crumbles.
Shuck oysters, discarding the top shell. Keep any oyster liqueur in the bottom half with the oyster. Top each with an equal amount of the filling. Squeeze a small amount of lemon juice on top, if desired. Set the oysters, shell side down, on a baking sheet and bake for 10–12 minutes. OR, set the oysters, shell side down, on the hot grill. For either method, cover and cook for 4–5 minutes or until the oyster liqueur just begins to bubble. Serve immediately.