Hi jw_wi,
What Gjstewart said is the correct way to format a UEFI partition. One thing I haven't seen in here is whether you're using ImageW or ImageX for your capture/deploy. It is very important that if you are doing a UEFI/BIOS cross-platform image that you use a file based imaging tool, in this case ImageX.
So, assuming you're using ImageX you can either use the UEFI script that Gjstewart is using, or if you are able to upgrade to 9.6 there is a "Create Default Partitions" sub-action in the Partition Action. This will auto-detect UEFI or BIOS and make a standard layout drive very similar to the script Gjstewart shows up above. Additionally for 9.6 I would highly recommend using the wizard to get started. Once that is done add in the additional actions you might need to customize it to your specific needs. If you are pre-9.6 then I would recommend using the diskpart script listed above.
Thanks!