Open a terminal and run the following command to list your hard drives

diskutil list

It should return something similar to the following

bobs-MacBook:~ bob$ diskutil list
/dev/disk0 (internal, physical):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        *1000.1 GB  disk0
   1:                        EFI EFI                     209.7 MB   disk0s1
   2:                  Apple_HFS Macintosh HD            999.1 GB   disk0s2
   3:                 Apple_Boot Recovery HD             650.0 MB   disk0s3

/dev/disk2 (external, physical):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        *8.0 GB     disk2
   1:                        EFI EFI                     209.7 MB   disk2s1
   2:                  Apple_HFS Install macOS Sierra    7.0 GB     disk2s2

bobs-MacBook:~ bob$

From above we see that the EFI partition on the main drive is disk0s1.

Make a directory for it to mount to

sudo mkdir /Volumes/TMPEFI

Mount it.

sudo mount -t msdos /dev/disk0s1 /Volumes/TMPEFI

It should now show up in finder for you to browse.

To unmount it simple eject it in Finder, or use one of the following commands

umount /Volumes/TMPEFI

diskutil unmount /Volumes/TMPEFI