Cut cheese into thin slices - it`s even faster if you buy the Gouda in slices. Also cut the tomatoes into slices.
Lay out or roll out the puff pastry on a baking sheet (if necessary on baking paper). Spread thinly with mustard. First put the cheese and then the tomatoes on the dough. Season with oregano, salt and pepper.
Bake at around 180 ° C for 10 to 15 minutes, until the cheese has melted and the dough has risen a little at the edge. It goes faster, of course, with a preheated oven.
Of course, it also works with other types of cheese, other mustard and other spices. Incidentally, if you do it right, you can hardly taste the mustard or not at all.
In my experience, the recipe also tastes good for people who actually don`t like mustard or tomatoes.