Add the fresh strawberries to a food processor and puree until smooth, you need 1 cup of strawberry puree.
Add the puree to a small saucepan and cook it over medium heat until it comes to a slow boil, stirring consistently, until it has thickened and reduced to about 8 tablespoons. This process will take about 10-15 minutes.
When the puree has thickened and reduced, transfer it to a measuring cup and allow it to fully cool before using it.
Add the butter to a large bowl and beat it until smooth.
Add half of the powdered sugar and mix until well combined, stop to scrape the sides and bottom of the bowl.
Add half of the strawberry reduction, and the vanilla extract, lemon zest, and salt whisk until well combined.
Add the remaining powdered sugar, beat until combined, and add the strawberry reduction as needed to get the right consistency.
Add frosting to a piping bag fitted with a star tip and pipe onto the cupcakes. Garnish with a fresh strawberry.
Chill for 1-2 hours before serving.
Serve at room temperature.