Put the fish on a baking dish and season with salt, pepper, lemon juice and lemon slices. Let it marinate for about 20 minutes.
Preheat the oven to 180ºC (350ºF). Drizzle the fish with 150 ml of the olive oil and bake for about 20 minutes. Occasionally, drizzle the fish with the sauce.
Meanwhile, put the parsley and the garlic in a food processor and pulse until well chopped. Put the mixture in a bowl, add the breadcrumbs and thyme and mix all ingredients.
Briefly remove the fish from the oven, sprinkle with the previous mixture and drizzle with the remaining olive oil. Put the fish back in the oven for about 10 minutes or until the crust starts to turn golden brown.