stuffed mushrooms w/ sausage
Because of the water in the cell structure, I don't think the mushrooms can be frozen without break down. The peppers should be able to be frozen without too many ill affects. Other peppers seem to be frozen on a regular basis without issue (poppers).
Recipe-wise I'd go this way:
Pull off the mushroom cap and reserve the stem.
Make your sausage and add the stem back into it as a binder. I'd go mild flavors in the sausage to match the cap. By mild I'm thinking a couple of cloves of garlic, a bit of sage (fresh) and some basil.
Finish with parmeasan and bake at 350 until browned.