Website not indexing
You need to tell Google that you have a new site or the best SEO in the world won't matter a jot; Google has no idea your site exists until you tell it.

There are 4 essential steps to getting your site indexed:


Add your URL – Submit your website for inclusion in Google's index.
App crawling – Get your app indexed by Google.
Search Console – Submit a Sitemap of your website to Google.
Structured data – Label your structured content to help users find pages relevant to their search.


These steps, and more, are detailed here.

Edit: I've taken another quick look at your site and I think you may be sending Google mixed signals about what to index.


You said your site is http://gastro-on-fire.be but that re-directs to https://gastro-on-fire.be -- These are two different sites.
Both sites are accessible also at the www subdomain, so you have actually 4 sites, which one do you want to index? Pick one, and follow Google's advice for that one. Add the others in Webmaster tools but set tell Google which is your preferred one, which one it should index.
Ensure your seo strategy is inline, and remains in line with that choice. Currently, the sitemap at https://gastro-on-fire.be/sitemap.xml gives all the site links as the www version; so you're telling Google to crawl the www site instead!!


Which one do you want to be indexed? Pick one, and ensure everything you tell Google backs up that choice.