Step 1Trim the ends off the cucumber and quarter it lengthwise. Slice one quarter in half down the middle to make a spear (about 5 inches long; it should be just longer than the height of a lowball glass). Roughly chop the remaining pieces and puree in a food processor. Strain the juice and discard the pulp.
Step 2In a lowball glass, combine 2 ounces (one-quarter cup) cucumber juice and a pinch of salt. Slowly pour in the Prosecco. Garnish with the reserved cucumber spear. Serve with a wedge of lemon, Tabasco and salt (for each person to add to taste).