Slice tomatoes. Drain oil off sardines.

Spread bread with margarine, put tomato slices, then put sardines.

Separate egg whites from egg yolks. Beat egg white until stiff foam, Mix egg yolks, mayonnaise and mustard. Mix with egg white.

Cover the sardines with this mass. Put the sandwiches on a baking tray lined with parchment and bake in an oven until golden crisp appears for 5-7 minutes. Serve immediately.