Preheat your oven to 210°C.
In a large bowl, prepare your crumble by mixing the flour, butter and pinch of salt until you get a crumbly dough.
Wash and finely dice the tomato.
Steam the fish for 5 minutes and crumble. In a salad bowl, mix the diced tomato, peas, chives, lemon juice and cooked fish pieces.
Spoon this mixture into an oven dish and sprinkle with the crumble mixture.
Put into the oven for 15 minutes.