Preheat oven to 300 degrees. In a medium saute pan, place bacon over low-medium heat for 2-3 minutes until fat begins rendering. Add shallots and garlic to pan, cook in bacon fat until slightly translucent.
Add White Wine and Spinach to pan and reduce by 1/2. Add Heavy Cream, Salt, Black Pepper, and Gruyere, once again reducing by 1/2-3/4. (You really want to reduce this one down to get all the flavor in your filling. While its reducing you can start shucking your oysters, discard the top shell of each oyster and leave the meat sitting in its own liquid in the bottom shell.) Last thing you want to do is remove the pan from the heat and fold in the butter, 1 tbsp at a time.
Top each half-shelled oyster with a dollop of Spinach filling. Place oysters on large baking pan topped with rock salt (It helps steady the oysters) in the oven or on the grill. Bake or grill for approximately 5-7 minutes in this fashion.
While the oysters are cooking, create the crumb topping in a small mixing bowl by combining dry cheese, bread crumbs, and parsley, then pouring melted butter over the top.
Remove oysters from oven and place a small spoonful of the crumb topping on each oyster. Return to oven or grill and bake until bread crumbs begin to slightly brown or about 8-10 minutes. Remove and serve.