General Recipe Trouble Shooting

I want to make a badass mushroom burger. I'm not talking about a portobello sandwich, I mean a burger with chopped up mushrooms as the body. Attempted it before and I liked it okay, but it's sort of fell flat with my wife. I have shiitake portobello and cremini mushrooms. Obviously, I would cook the mushrooms down first, probably just roast them in a hotel pan because it's quicker and easier. I will season them in there. Any thoughts on binding/cooking? I used egg and breadcrumbs last time, open to any suggestions.