Preheat oven to 450 degrees F.

Melt butter in a saucepan over medium heat. Cook onion and garlic in butter until soft. Reduce heat to low, and stir in spinach and Monterey Jack cheese.

Cook until cheese melts, stirring frequently. Stir in the cream, and season with salt, pepper and Worcestershire.

Place oysters on a baking sheet. Spoon sauce over each oyster, just filling the shell. Combine almond flour and Parmesan cheese in a small bowl. Sprinkle topped oysters with almond flour-Parmesan mixture.  

Transfer to oven and bake for 10 minutes or until cooked through. Change to broil and broil 1-2 minutes to golden.

Serve.