Peel oranges so that the white skin is completely removed. Cut out the fillets from the parting skins. Collect the juice and mix with vinegar and oil. Season to taste with sugar, salt and pepper.
Clean and wash the fennel and cut into thin slices. Clean, wash and cut the salad into bite-sized pieces, arrange on plates with the fennel slices and orange fillets. Pour orange vinaigrette over the salad and serve.