Don't see why you can't make the standard "green bean casserole" and add sauteed sliced fresh mushrooms to it.
I just put together my casserole.
1 small can French fried onions, divided
2 (16-oz.) cans French-cut green beans, drained
1 tsp. soy sauce, low-sodium if desired
1/2 cup milk
1/4 tsp. freshly ground black pepper
1 (10 3/4-oz.) can condensed cream of mushroom soup
In a medium bowl, combine soy sauce, milk, pepper, and soup. Whisk to blend. Add drained beans and half a can of onions. Mix well. Top with remaining onions. Bake in a preheated 350 degree oven until hot and bubbly. Serves 4
I see no reason why you couldn't add sauteed mushrooms to the above recipe. I think it would be particularly good. I love mushrooms and would include some in my green bean casserole if I had any. You've given me an idea.
"As a girl I had zero interest in the stove." - Julia Child
This is real inspiration. Look what Julia became!