Half fill a frying pan with water and bring to the boil over high heat. Add the chopped lemon and salt. Add the fish and poach 5-7 minutes until just cooked through. Drain and set aside, discarding the lemon.
Place the zucchini in a bowl with basil, mint, chillies, green onions and olive oil. Combine and season. Break the fish into chunks and add to the salad with the lemon and lime juice. Gently combine.
Serve immediately with mayonnaise and crusty bread.