Preheat oven to 375 degrees F. Lay the puff pastry out on a baking sheet. Prick all over with a fork.
Pop in the oven for 10-12 minutes or until the crust starts to turn light gold. Remove the pastry from the oven, pressing the center down with a fork, if it puffed up a bit.
Meanwhile mix tuna and mayonnaise with fork. Season with salt and pepper.
Spread the mustard across centre. (I use mustard "a l'ancienne).
Spoon the tuna mix on top.
Combine eggs with sour cream and mix together. Season with salt and pepper.
Pour over tuna.
Slice tomato and arrange them on top of your quiche. Sprinkle with cheese.
Bake for 30 minutes or until quiche is golden brown.