Preheat oven to 220C
On a large baking tray, scatter slices of potato, tomatoes and red onion and half of the lemon slices. Drizzle with 1tbs olive oil and season with salt, then toss on the tray so everything is evenly coated with oil and salt.
Remove a handful of nice leaves from the coriander and dill leaves, set aside then cut the remaining bunches in half.
Using paper towel, pat the trout inside and out of any excess of moisture. Place the trout on the baking tray on top of the vegetables. Season the cavity with salt and pepper then fill with herbs and remaining lemon slices.
Using a sharp knife, make 3 slashes on each side of the fish, about 2cm deep.
Drizzle olive oil over the fish and a sprinkle a four finger pinch of extra salt.
Bake the fish in the hot oven for 15 minutes, then turn the temperature down to 180ºC and cook for a further 20 minutes.
Remove from oven and a big green salad and preserved lemon mayonnaise.
Preserved Lemon Mayonnaise
Whisk the egg yolks, Dijon mustard and lemon juice in a bowl.
Gradually whisk in the olive oil and vegetable oil in a thin, steady stream until thick and emulsified.
Add the preserved lemon and stir until combined. Store in an airtight container in the fridge for up to 1 week.