Cook the strawberries with the water and lemon juice over medium heat until they are soft. Purée the warm berries and strain through a wire mesh strainer to remove the seeds. Return the purée to your cleaned pan and add the sugar and vanilla seeds. Cook the mixture over medium heat until it is thickened, stirring frequently to avoid burning. Fill hot jars with syrup, cool, and store in the refrigerator for up to 1 month, or prepare canning jars and process in a hot water bath for 10 minutes. To serve, fill a glass with a shot (11⁄2 to 2 oz) of syrup, torn mint leaves, and top with seltzer or prosecco. Stir to combine and enjoy!