As a substitute teacher, I often email multiple teachers in need of a substitute, asking them to send me their lesson plans ( I prefer to actually teach). Often by the time the/several teacher(s) send me their plans, someone else has picked up the assignment. I suggest you implement a feature to allow teachers to post assignments to a list of pre-selected substitutes, giving them first right of refusal or acceptance, via an automated email containing a link to the assignment. If nobody on that list accepts within some fixed period, then the assignment is published for all to see.
I believe this would be an easy feature to program. If you need help doing this, please let me know.
Be well,
George Gluck
MCPS, STEM and Social Studies Substitute