Add a few pieces of ice to a wine glass - you can fill part way or more, as you prefer.
Pour the limoncello over the ice then add the prosecco. Top up with the sparkling water/club soda and gently stir to mix without loosing too much of the bubbles. Optionally garnish with a slice of lemon. You can also garnish with a sprig of basil, mint or thyme as you have and prefer.