Cut avocados in half and remove the stone and discard. Dip the avocado in the reserved UGLI® tangelo juice to prevent browning. Scoop out a little flesh and chop. Mix together the avocado flesh, UGLI® tangelo and mussels and spoon back into the hollows. Chill. Meanwhile mix the egg yolks, sugar and mustard in a bowl. Slowly whisk in the oil until thick and creamy. Season well. Add the UGLI® tangelo juice and half the rind. Spoon the mayonaise on top of the filing.