Heat 2 tablespoons of the oil in a frying pan, add the shallot and garlic and cook for 2–3 minutes. Add the spinach and stir until wilted. Add the Pernod, if using, and cook until the liquid has been absorbed.
Cover the base of a roasting tin with rock salt, then arrange the oysters on top. Spoon the spinach mixture on to the oysters. Mix together the breadcrumbs and cheese, then sprinkle over the spinach.
Drizzle with the remaining oil and bake in a preheated oven, 200°C (400°F), Gas Mark 6, for 10–15 minutes until lightly golden.