It doesn't show off mushrooms all that well, but I make this filling pretty often for my son:
https://jamiegeller.com/recipes/isra...kets-bourekas/
Basically, it's any mushrooms. I typically buy pre-sliced ones on markdown. Any onion. Lots of red pepper.
Turns out frozen Pepperidge Farms Puff Pastry is Vegan! Makes an excellent hot pocket. Also a good filling for tamales or dumplings or humbao.