Baked fish with piquant salsa

For the salsa:

6 tbsp rice vinegar or white wine vinegar

2 tbsp fish sauce (found in most supermarkets)

50g sugar

400g tinned, chopped tomatoes

1 cucumber, de-seeded and chopped into 1cm/½ in pieces

1 small red onion, peeled and finely chopped

1 spring onion, trimmed and finely chopped

1 red chilli, de-seeded and finely chopped

Juice of ½ a lime

2 tbsp chopped fresh coriander

1 tsp finely grated fresh ginger

For the fish:

4 x (150g-175geach) fish, such as salmon, tuna, mackerel, mullet or sea bass, off the bone but leave the skin on if you wish

Salt and freshly ground black pepper