Heat EVOO in the same pan used for the fish over low heat. Add the garlic, lemon zest and some salt and pepper, stir for 2-3 minutes until soft but not coloured. Stir in the tomato, anchovy, capers, vinegar and sugar, then partially cover with a lid (or foil). Cook for 3-4 minutes until the tomatoe softens. Now add the olives and parsley.