Mackerel with tomatoes and tapenade

4 fresh mackerel fillets

4 large ripe tomatoes, thinly sliced

1 tsp thyme leaves

salt

pepper

For the tapenade dressing:

30g kalamata olives, stones removed

2 anchovy fillets in olive oil, drained

1½ tsp capers in brine, drained and rinsed

1 small garlic clove, crushed

4 tbsp extra virgin olive oil

1 tbsp red wine vinegar

flat parsley sprigs