You can use the below command to retrieve the environments under a specific lab:
Get-AzureRmResource -ResourceGroupName devlab1 -ResourceType 'Microsoft.DevTestLab/labs/users/environments' -ResourceName "devlab1/@all" -ApiVersion '2016-05-15'
Executed above command below is the sample output:
I have extracted that piece of code from below modules:- (It has got good amount of code , you just need to tweak it based upon your requirements)
Section:
Regards,
Shiva.