Remove the skin of the cod and soak in water for 24 hours in the fridge, changing the water often (at least 4 times).
On the day you are making the dish, fill a large pot with water and add large chunks of the cod. Bring to the boil; scoop out the fish as soon as the water starts to boil. In the same water, cook potatoes until tender (but not falling apart). Slice the cooked potatoes into thick slices.
Preheat oven to 180 C / Gas 4. Brush a 20x30cm roasting dish with oil.
Layer the ingredients in the dish in the following order: cod, potatoes, peppers, palm hearts, tomato and onion. Drizzle everything with olive oil, sprinkle oregano and scatter the olives on top. Bake in the preheated oven for 30 minutes.