Cook the lentils in gently boiling water for 10 minutes, then strain.
Fillet the oranges and place in a bowl. Squeeze the juice out of the orange remnants over the fillets by hand.
Peel the onions and cut into strips. Lightly sweat the onion strips in hot olive oil, add the lentils, deglaze with balsamic vinegar and orange juice. Season to taste with salt and pepper. Stir in the finely chopped parsley and finally fold in the orange fillets.