Fill a wine glass with ice cubes (covered, but not a mountain above the glass).
Then pour prosecco into the glass. Add Aperol and finally top up with soda.
The Aperol Spritz will be especially good if a soda siphon (like a whipped cream bottle) is used for the soda. Place the siphon on the rim of the glass so that the soda creates a swirl and the liquids mix well.
Add a few ice cubes at the end, if necessary, so that the glass is full again.
Serve with the orange slice and a straw.