Hi Roger,
This is indeed very simple to achieve. We have many implementations similar to this:
1. Create a PortGroup on your vSwitch or dvSwitch Called "Fortinet Trunk" or something similar
2. Edit the PortGroup and change the VLAN to be "VLAN Trunking", in the "VLAN Trunk Range" field enter all of the VLANS you will require
3. On your Fortinet device Assign one of the interfaces to the "Fortinet Trunk"
4. On the Fortinet setup sub-interfaces for each vlan
5. Create a new Port Group for each VLAN, edit the PortGroup to include the VLAN ID (your VMs will sit on this)
That should be all you require to get this up and running, any questions or issues please let me know. I can assist further if required.
Regards
Steve