This is the default layout provided by the EzPublishLegacyBundle. To override it, you can use the following configuration:
# In ezpublish.yml or any imported config file.
# Replace "my_siteaccess" to a valid SiteAccess or SiteAccess group name.
ezpublish_legacy:
system:
my_siteaccess:
view_layout: YourBundle::pagelayout.html.twig