1. Preheat the oven to 200 °C (390°F).
2. Peel onions and garlic, slice it roughly
3. Use a grater to get the zest of one whole lemon and squeeze the juice of half a lemon
4. Combine everything but the fish in a food processor or a blender and process into a salsa like consistency.
5. Cover fish with the herb marinade on both sides and a little inside the fish cavity. Add a few lemon slices...