1. Preheat oven to 350ºF and adjust rack to middle position.
2. Place feta, zests, chili flakes and orange juice in a bowl. Gently combine.
3. Pour into an oven-proof bowl and drizzle with olive oil.
4. Place watermelon slices on four salad plates. Divide warm feta on top of each piece of watermelon. Evenly divide the salad and place a portion on top of the feta.
5. Drizzle with balsamic.