Add sliced strawberries and simple syrup to a shaker and muddle until very juicy.
Add limoncello, fresh lemon juice, and ice. Shake 10–15 seconds until well chilled.
Strain into a wine glass or champagne flute filled halfway with ice.
Slowly add prosecco to preserve bubbles; optionally add a splash of sparkling water or club soda.
Stir gently and garnish with strawberry slices or a lemon twist. Serve immediately.
Notes
Chill ingredients and glassware for maximum fizz. Adjust sweetness with more lemon juice if needed. Use a dry prosecco to keep the drink balanced. Make the strawberry base ahead, then top with prosecco just before serving.