Preheat the oven to 400°F. Line a baking sheet with parchment paper.
Heat the olive oil in a medium-size sauté pan over medium heat. Add the onions, celery, and pepper, season with salt and cayenne, and cook, stirring, until the vegetables are wilted, about 2 minutes. Add the garlic and shrimp and season again with salt and cayenne. Cook, stirring, for 2 minutes, then remove the pan from the heat.
Pour the mixture into a medium-size mixing bowl. Stir in the water and enough bread crumbs to bind the mixture. Add the parsley and season again to taste with salt and cayenne. Set aside.
Place each flounder brown side up on a cutting board. With a sharp boning knife, cut along the center bone of the fish. Carefully peel open the fish, pulling the flesh back to form a pocket. Season the outside and pocket of the fish with Essence.
Divide the stuffing mixture into four equal parts and fill the pocket of each flounder with it. Fold the flaps over the stuffing.
Place the fish on the prepared baking sheet. Drizzle with the melted butter and bake until the fish flakes easily with a fork, about 20 to 25 minutes.
Yield: 4 servings