I've been a member of the same peer speculative fiction writing workshop for decades now. In addition to the usual stories and novels, we've commented on plays intended for the stage, plays intended for historic sites, essays, and other forms of prose.
A couple of our members like submitting outlines of something they are planning to write. These pose some specific challenges to a workshop, so I thought I'd run through some suggestions on how to get the most out of your workshop if you feel like doing something like this.
First, recognize that this does impose a lot of extra cognitive work on your workshop. We're used to reading, thinking about, and analyzing completed prose works. No matter what their failures, gaps, ambiguities, and errors, we can usually tell what you're driving at, and do our best to help you move in that direction more effectively. A completed prose work is something that has actually been written with the intent of having someone else read it.
By contrast, an outline is, by definition, not meant for anyone to read. It is a guide to yourself on how to proceed. In writing it you have not done the threatening work of daring to write something meant to entertain someone else.
So you have to turn your outline into something meant for someone else to read, which is almost as much work as writing something. I've sometimes read an outline and had absolutely no idea of whether that set of events would work on the page. That's because I sometimes don't know this about my own work, using an outline I wrote myself for myself.
So: provide capsule descriptions of the characters, their roles, their goals, and their arcs. Explain not what a setting looks like, but what it feels like, what role it plays in the story. Be explicit about what is untold and suspenseful, what is obvious about a character and situation, and what revelations will come as a surprise to the characters, or to the reader.
I do this in my work as a marketing writer. I tell my client what the goal of each part is, who I am assuming the reader is, what I am trying to get them to think, and then to do. Knowing what the piece is trying to do lets them focus on the things they know about, their business, and also distracts their attention from what they would otherwise waste their time on, monkeying with the prose (that is, invariably, making it longer and vaguer).
If you do this, you'll find that you have to do a lot of extra work before you submit the outline to your workshop. Maybe you'll decide it's not worth it, and that you should just use the outline to write the damn thing. That's usually the best idea, by the way. Or you might decide that you really can't figure out some crucial things, and would really like to talk it over with the group. Give them something they can actually talk about.
A workshop is a wonderful servant and a terrible master. It is powerful, but limited. It can get cranky if you misuse it, because everyone is busy. Our workshop has survived for decades because we recognize how much everyone puts into it, and how that benefits each of us.
So, think twice about submitting that outline, and if both thoughts really do confirm that you need to do it, make sure provide your workshop with the tools it needs to do its best work for you.