Baked Cod with Harrissa on Potatoes and Tomatoes

This recipe is my variation of one of Claudia Roden's in her book Arabesque. It's a great book I can highly recommend.

To serve 2
a big dollop of harrissa - Belazu rose harissa is my favorite
juice of half a lemon
2 thick pieces of cod fillet
about 300g of small potatoes such as charlottes, scrubbed and cut into 1cm slices
2 large tomatoes cut into quarters
half a red onion finely chopped
extra virgin olives oil

Mix the harissa, lemon juice and some olive oil in a bowl then add the cod pieces and make sure they are covered with the mixture. Leave in the fridge to marinade for a couple of hours turning for time to time.
Pre-heat the oven to about 200 C.
Put the potatoes on to boil.
Put a splash of olive oil in an oven proof dish and add the onions. Put the dish in the oven for five minutes or so. Remove from the oven and scatter the tomato quarters in the dish. When the potatoes are just starting to go soft drain them and leave to dry out for 5 minutes or so and then add them to the dish. Season and give the dish a good shake to mix in the onion, oil and tomatoes with the potato slices.
Put back in the oven. After about 30 minutes move the contents of the dish around a bit to ensure the potatoes get evenly browned and mix in the juices that will have come out of the tomatoes by now.
Cook for another 15 minutes and then put the marinated cod on top spreading any remaining marinade over the potato mixture.
Cook for about another 15 minutes until the cod is done.
Serve with a green salad.