Preheat oven to 375 degrees F with the rack in the middle.
Prepare a baking sheet with parchment paper or a silicone liner.
In a bowl squeeze juice from one of the mandarins over the carrot slices. Toss carrot slices with juice, mandarin segments, oil, salt, and pepper. Sprinkle with chopped rosemary.
Bake for 25-30 minutes until everything is softened and slightly browned. Serve with some more fresh rosemary.