cooking spray
3 tbsp. grated Parmesan cheese
1/4 cup whole-wheat panko
1/2 tsp. kosher salt
1/2 tsp. black pepper
2 tbsp. heavy cream
1 cup unsalted chicken stock
1 tbsp. all-purpose flour
1/2 cup chopped onion
3 cups sliced fresh mushrooms
2 tbsp. canola oil
12 oz. haricots verts