Put 1 tablespoon of olive oil into a pan on medium heat and sauté the onion, fennel and chili for 2 to 3 minutes, to soften. Add the tomato purée and cherry tomatoes. Simmer for a further 4 to 5 minutes. Season to taste with a little salt and pepper.
Arrange the fish fillets in the pan, on top of the tomato sauce. Cover with a lid and simmer for 8 to 10 minutes, or until the fish is cooked and starting to flake. Just before serving, carefully stir in the olives and baby spinach and heat for a further minute.
Meanwhile combine the parsley, garlic, lemon zest, and juice in a bowl.
To serve, arrange the fish fillets on plates and spoon over the tomato sauce. Sprinkle with the herby topping, and add a squeeze of lemon juice to finish.
Enjoy this with some additional steamed greens.
