Method:

1. Preheat oven to 175 °C.

2. Cut pork into 1/4-inch slices lengthwise, stopping 1/2-inch from the bottom, so it can fan out like a book. Stuff tomatoes, onion, and Gouda cheese in between the slices.

3. Combine garlic and salt in a bowl, then stir in mustard and pepper. Spread mixture all over the pork. Press pork slices firmly together and wrap in aluminum foil.

4. Bake in the preheated oven of 220 °C for about 1 hour 30 minutes. Uncover and continue baking in an over of 175 °C until nicely browned, about 30 minutes more.