Clean and wash the fennel and cut into fine strips. Finely chop the fennel greens and set aside.
Peel and fillet the oranges. Set the fillets aside. Catch the rest of the juice. If the oranges are untreated, rub the peel before filleting 2 oranges. Set the abrasion aside.
Peel the onions and cut into fine strips.
Heat the oil in a deep pan. Fry the fennel and onions, season with salt and pepper. Sprinkle the sugar on top. Deglaze the whole thing with the orange juice and add the orange zest. Possibly add the cinnamon and gently reduce the juice.
Finally add the orange fillets and just let them warm up. Season everything again with salt, pepper and sugar.
Sprinkle the fennel greens over the vegetables before serving.