Preheat grill.
Spread the Ryvita Sunflower seeds and oat crispbread with a little butter
Grill the fish fingers on each side for about 6 minutes.
While the fish fingers are grilling cook the peas in boiling water for about four minutes. Drain them and mash them with a potato masher or fork.
To make the tartare sauce mix together the mayonnaise, gherkins, yoghurt and capers. Stir half of the sauce into the pea mixture.
Spread the pea mixture on top of the Ryvita, add a fish finger and top with the rest of the sauce. Sprinkle with black pepper