Pour 2 tbsp of the oil into a large, shallow pan with a lid and put over a medium heat. Add the onion and potatoes, cover and cook for about 5 mins, stirring occasionally until the onion has softened. Add the remaining oil, garlic and spices, and cook for 2 mins more. Pour over the lemon juice and sizzle for a moment. Add the tomatoes and half a can of water, then crumble in the stock cube. Season with a little salt, then simmer for 15-20 mins until the potatoes are just cooked.

Stir in the prawns and fish, and scatter the mussels over the top. Cover again and cook for about 8 mins, stirring gently once or twice. While the stew is simmering, mix the parsley and lemon zest together. When the mussels have opened and the fish is just cooked through, take off the heat, scatter over the parsley mixture and drizzle over a little more oil. Serve straight from the pan with crusty bread on the side.