Wanting to make this but guests just informed me that they don't like mushrooms...can I add sausage? or do half substituting zucchini?

Sure! This is a very flexible recipe. I would use loose sausage and brown it well first. Same with zucchini-- sauté it first in some butter. I like the idea of sausage more than the zucchini. As ChefJune says, the zucchini is pretty bland. Let me know what you do and how it turns out!

I can't imagine why you couldn't sub cooked sausage for the mushrooms. I wouldn't use zucchini as a sub - it's pretty bland in flavor compared to mushrooms, and also can be watery.