Preparation 15 minutes, cooking 20 to 40 minutes.
Bake the fish whole. If you want to cook it in salt, ask the fishmonger not to remove the scales. Sprinkle a handful of salt on the bottom side of the fish and a handful on the top side. Alternatively, grease with a drizzle of olive oil and bake at 180 degrees. Cooking time depends on the weight of the fish and the oven used. Ask the fishmonger for advice. It is always preferable to cook fish in the oven at a medium temperature, never high. Generally, the fish is ready when you observe water coming out of its mouth. If using fish fillets, cook them in a pan with a drizzle of olive oil.
Prepare a pesto with arugula (or basil) leaves, olive oil and a pinch of common salt. Pour the arugula in a blender and reduce it to a cream, adding the olive oil little by little. Season the pesto with salt and pepper.
Pour it over the fish before serving.