Boil about eight cups of water.
Place the oysters in a shallow pan. Pour the boiling water over them. Leave for two minutes. Strain.
Pry the shells open. Discard the empty halves.
Preheat the oven to 400F.
Melt the butter in a pan. Saute the onion and garlic. Pour in the yogurt. Add the spinach. Cook just until bubbly.
Grate the cheese.
Spoon a little of the yogurt-spinach sauce over each oyster. Sprinkle with cheese and bread crumbs. Bake for about two minutes or just until the cheese melts. DO NOT bake for too long or the oysters will shrivel and dry out.
Serve the oysters preferably with a good white wine.