Thaw the spinach in colander squeeze as much of the water out as possible. Mix spinach, Parmesan, and mayonnaise in a bowl until creamy.
Texture should be thick, if you overdo the mayonnaise add more Parmesan. Split oysters in half and line on a cookie sheet or in a baking pan. Top each oyster with enough of the spinach mixture to cover. Cut bacon with kitchen scissors, large enough to drape over top of oyster.
Bake in a preheated 350 degree F oven until bacon is crisp. Serve hot.