Hello Carlos,
In order to generate the Windows 2016 image for UEFI, you need to use the DiskLayout parameter:
New-MAASImage -WimFilePath $wimFilePath -ImageName $image.ImageName -MAASImagePath $targetPath -SizeBytes 20GB -Memory 2GB -CpuCores 2 -DiskLayout "UEFI"
Similar for the Windows Nano Server image generation:
.\NewNanoServerImage.ps1 -IsoPath $isoPath -TargetPath $targetPath -AdministratorPassword $password -Platform BareMetal -Compute -Storage -Clustering -MaxSize 1500MB -AddCloudbaseInit -AddMAASHooks -DiskLayout "UEFI"
Moreover, here is more information on how you can patch the grub2 in MAAS, if you are using Hyper-V Generation 2 VMs as MAAS nodes.:
http://wiki.cloudbase.it/maas
http://wiki.cloudbase.it/hyperv-uefi-grub
A full video tutorial of Hyper-C where Hyper-V Generation 2 VMs are used(with UEFI) can be found here: https://www.youtube.com/watch?v=jgApG...
Adrian.