Heat the oil in a large pan and cook the onion, garlic and fennel seeds for 5 minutes, until softened. Stir in the smoked paprika and cook for another 2 minutes.
Add the fish stock, chopped tomatoes and new potatoes, bring to the boil and cook for 15-20 minutes, until the potatoes are almost done.
Add the frozen fish fillets to the pan, bring back to the boil and simmer gently for another 8-10 minutes, or until cooked through. Break up the fish a little as you stir and season.
Mix the parsley and lemon zest. To serve, spoon the stew into 4 bowls and scatter over the parsley and lemon mixture. Serve with lemon wedges.