In a saucepan, sauté the finely chopped onion and peeled and chopped garlic in olive oil with the salt and pepper. Add the diced potato, bay leaves, cinnamon, and nutmeg. Cover with the stock and cook for around ten minutes.
Next, add the spinach and diced tomato and aubergine, and continue cooking over a low heat until the vegetables are tender (add more stock if needed). Just before turning off the heat, add the horse mackerel in pieces (set aside 4 whole horse mackerels for garnishing). Cook for just a few more minutes, then take off the heat and correct the seasoning.
Remove the bay leaves and serve very hot, garnished with the finely chopped chilli pepper and herbs.