In a medium skillet, render the bacon until crispy. Transfer the bacon to paper towels to drain until cool, then chop and reserve separately. To the fat remaining in the skillet, add the onions and sauté on low heat until the onions are caramelized. Season with salt and pepper. Add the butter and the flour to the sautéed onions and cook, stirring, for 2 to 3 minutes, to form a blond roux. When the roux looks like a wet beach, whisk in the heavy cream. Bring the mixture to a simmer and cook for 5 to 10 minutes, until any grainy texture of the flour has cooked out of the roux. Season with Creole Seasoning to taste. Add the chopped crispy bacon and set aside to cool. Add the spinach and mix well.

Preheat the oven to 400°F. Line a large baking sheet with kosher or rock salt and set aside.

Place the oysters (on their shells) about 1 to 2 inches apart on the baking sheet. Top the oysters with the cooled spinach mixture. Sprinkle each oyster with some of the Parmesan Bread Crumbs and bake until golden brown and bubbly, usually about 20 minutes. Serve immediately.