In a small saucepan, combine the chopped strawberries, sugar, and water.
Bring the mixture to a boil over medium heat, stirring occasionally.
Reduce the heat and let it simmer for about 10 minutes until the strawberries are soft and the syrup has thickened.
Strain the syrup through a fine mesh sieve into a bowl, pressing down with a spoon to extract all the liquid. Let it cool.
In a champagne flute, add 2 tablespoons of the strawberry syrup and 3 tablespoons of lemonade.
Top with chilled prosecco and gently stir to combine.
Garnish with a fresh strawberry or a lemon slice, if desired.