Making the pineapple juice mixture: Pour the pineapple juice into a bowl. Cut the vanilla beans in half lengthwise and scrape the seeds into the pineapple juice. Whisk gently to separate the seeds and to blend.
Run the lime wedge around the top of 4 champagne flutes and rim with the crushed coconut flakes. Pour 3/4 cup of the pineapple juice and 1/2 cup of the prosecco into each glass. Decorate with fruit as desired.