In a small bowl combine the spinach, onion, Parmesan, butter, wine,cayenne pepper, and black pepper. Shuck the oysters and leave them on the half shell. Top with a heaping tablespoon of the spinach mixture and arrange them on a baking sheet.
Bake for approximately 10 minutes.
Remove from theoven and top each with a slice of tomato and cheese. Return to the oven and bake until the cheese melts.
Transfer the oysters to a serving platter and serve with a wedge of lemon andgood hot sauce. Enjoy!