Clean and wash the fennel, peel the onions. Finely slice both. Peel garlic and chop finely. Peel oranges so that the white skin is completely removed. Remove the fillets with a sharp knife between the parting skins. Squeeze the juice out of the parting skins and collect it.
Clean and wash the radicchio and cut into fine strips. Drain the olives. Whisk vinegar with orange juice, garlic, salt, pepper and sugar. Add oil and season to taste again. Mix all the prepared salad ingredients with the vinaigrette, set aside