Replied to a tweet by Matthias Ott Matthias Ott (Twitter)
Oh, we’re reading you Tania Rascia (@taniarascia)! Even easier for you it looks like Chris Biscardi (@chrisbiscardi) has already built out some infrastructure for webmentions on Gatsby(@gatsbyjs).
https://indieweb.org/gatsby#Plugins

Chris has written a bit about his process as well: Building Gatsby Plugin Webmentions.