Preheat oven to 450F/230C. Lightly scrunch a piece of foil and put it in a baking dish big enough to hold all of your oysters so it covers the dish.
First, shuck the oysters and loosen the meat from the shell. Pour off the liquid, setting it aside. Place the oysters on the foil in the baking dish so they are sitting flat.
Roughly chop the spinach, watercress or arugula/rocket and thinly slice the scallion/spring onion. Finely chop the garlic.
Melt the butter in a small skillet/frying pan. Add the spinach, watercress/arugula, scallion and garlic. Cook, stirring for a couple minutes so everything softens and the liquid largely evaporates.
Add the pernod, lemon juice and hot sauce. Stir through and cook a minute more so the liquid evaporates then remove from the heat.
Spoon a heaped teaspoon over each oyster then top with a little parmesan.
Bake for approx 8-12 mins until the top is lightly browned.
Many recipes include breadcrumbs in the topping - if you'd like to add some, mix a couple tablespoons with the cheese before you put it on top of the greens mixture. It will give a little crunch to the topping.