Wash the mint, remove the leaves and chop finely. Pour the vinegar and olive oil into a mixing bowl and add the mint. Season and mix. Blanch the tomatoes, cut into rounds and lay in a shallow bowl. Pour the contents of the mixing bowl on top. Cover with plastic wrap and marinate in the refrigerator. Remove the rind from the Munster cheese and cut into thin strips. Preheat the oven to 400°. Open the oysters and remove from the shells, taking care to keep their water. Filter the water, bring to a boil and poach the oysters in it for 15 to 20 seconds. Drain on paper towels. Cut the sheets of brick pastry into 4 and brush with melted butter. In the middle of each sheet of pastry, place a piece of Munster, a pinch of cumin and the poached oysters. Fold the brick pastry over, and brush the surface with butter again. Bake until the brick pastry just barely starts to change color. Lay the marinated tomato slices on a serving dish and place the pastries in the center of each.