Preheat oven to 375 degrees F.
In a large saute pan heat 1 tablespoon of the oil. When the oil is hot, add the sausage and cook, stirring occasionally for about 4 to 6 minutes. Add the onions and continue to cook for two minutes. Add the garlic, and continue to cook for 1 minute.
Remove from heat and transfer to a mixing bowl and let cool. Stir in the remaining olive oil, bread crumbs, parsley and cheese and mix well. Season the oysters with salt and pepper. Grease a 9-inch gratin dish or pie pan. Line the bottom with the oysters. Cover the oysters with the sausage mixture, packing it down onto the oysters. Place in the oven and bake for 8 minutes or until the top is golden brown. Remove from oven and serve warm.