hiera and variables inside a string - possible?

init.pp

class timezone (
  String           $timezone = 'Etc/UTC',
  Optional[String] $timezone_update = undef
) {
  # data from hiera with a variable inside?
  if $timezone_update {
    exec { 'update_timezone':
      command => $timezone_update,
    }
}

os.yaml

# Different commands per osfamily within the same module
# on some systems, the timezone is required 
# Gentoo
timezone::timezone_update: 'emerge --config timezone-data'

# Debian
timezone::timezone_update: 'dpkg-reconfigure -f noninteractive tzdata'

# Suse, needs value of timezone
timezone::timezone_update: 'zic -l ${timezone}'

# RedHat >= 7, needs value of timezone
timezone::timezone_update: 'timedatectl set-timezone ${timezone}'