Preheat your oven to 400°F (200°C). Roll out the puff pastry on a lightly floured surface to your desired thickness (about 1/8 inch thick). Transfer the rolled pastry to a parchment-lined baking sheet.

1. Sprinkle shredded mozzarella (or goat cheese) evenly in the center of the pastry, leaving a border around the edges. Arrange the sliced tomatoes over the cheese, overlapping them slightly. Drizzle olive oil over the tomatoes and season with salt, pepper, and garlic powder.
2. Gently fold the edges of the pastry over the tomatoes to form a rustic crust. The center should remain open to showcase the tomatoes.
3. In a small bowl, whisk the egg with 1 tbsp of water and brush it over the edges of the pastry. Bake in the preheated oven for 30-35 minutes, or until the crust is golden and the tomatoes are tender.
4. Once out of the oven, drizzle the galette with balsamic vinegar (if using), and garnish with fresh basil and thyme or rosemary. Let it cool slightly before slicing.
5. Serve warm or at room temperature, and enjoy!