Adjust the racks to the middle of the oven and preheat to 475 degrees F. Spray a half baking sheet with nonstick spray.
Add the sweet potato to a large bowl and toss with the red onion, rosemary, 2 tablespoons olive oil, salt and pepper.
Flour your work surface and stretch the dough out to an oblong rectangular shape. (You may need to use a rolling pin.) Place the dough on a sheet tray and top with the sweet potato mixture in an even layer. Drizzle with 1 tablespoon of olive oil and scatter the slices of brie.
Bake until golden and crisp, 15 to 17 minutes. Slice into wedges and serve.