Preheat your oven to 400°F (200°C). In a mixing bowl, combine whole wheat flour, baking powder, and salt. Stir until well mixed. Add Greek yogurt and olive oil, mixing until a dough forms. If sticky, add more flour.
Turn the dough onto a floured surface and knead gently for about 1 minute until smooth. Roll out into a rectangle about 1/4 inch thick. Cut into smaller flatbreads and place on a baking sheet lined with parchment paper. Lay slices of Brie on top.
Spread cranberry sauce over each flatbread, covering the Brie. Sprinkle chopped rosemary and walnuts if using.
Bake in the preheated oven for about 15-20 minutes until cheese is melted and edges are golden brown.
Let cool for a few minutes, drizzle with honey if desired, slice, and serve warm.