Preheat the oven to 400 degrees F and line a baking sheet with parchment paper.
Slice the tomatoes and place on a paper towel-lined baking sheet. Sprinkle with salt and top with another paper towel.
Place the defrosted puff pastry on the baking sheet. Cut a 1/2 in. border. Puncture the pastry a few times with a fork.
Spread the mustard over the puff pastry, staying within the border. Top with sliced brie, grated parmesan cheese, and herbs de Provence. Arrange the sliced tomatoes on top, sprinkle with salt, and drizzle with olive oil. Brush an egg wash along the border, and sprinkle with parmesan cheese.
Bake for 35-40 minutes, rotating the baking sheet halfway through baking.
