You can make the pureed vegetable topping up to a day in advance. You can prep the crostini earlier in the day, as well. Just assemble the bruschetta just before serving to ensure the bread doesn't get soggy.
You can also keep this vegetarian by swapping out the prosciutto for thin shavings of Parmesan or Asiago cheese if you prefer. You want something to give a salty bite to the appetizer, whichever route you go.
For more tips and tricks, be sure to read the full article above.