Preheat oven to 350 degrees.
Spray a medium saucepan liberally with cooking spray then warm over
medium heat. Add ¼ cup finely diced white onion and mushrooms and sauté until
onions are translucent and liquid has released from mushrooms.
Sprinkle onion/mushroom mixture with coconut flour, stirring in one
teaspoon at a time until each is incorporated.
Add vegetable broth and milk, stir well to combine and bring to a gentle
rolling boil. Reduce heat and simmer, stirring occasionally until the mixture
has thickened or reduced by about half. (You can blend it smooth with an
immersion blender if you want, but it isn’t necessary.) Set aside.
Reduce two slices of bread to crumbs using a food processor. Add
Parmesan cheese and pulse again until well blended.
Spray a medium skillet liberally with cooking spray then warm over
medium heat. Add ½ cup finely diced white onion and saute until translucent.
Sprinkle onions with breadcrumb and cheese mixture, stirring in a little
bit at a time until everything is incorporated (this keeps the crumbs from
getting soggy). Sauté until everything is a rich, golden brown.
Grease a casserole dish and pour the slightly cooled soup mixture into
the bottom. Add the green beans and ⅓ of the breadcrumb mixture. Stir to
incorporate. Season with salt and pepper to taste.
Top the bean and soup mixture with the remaining breadcrumb mixture.
Bake uncovered for 30 minutes, or until heated through and still golden
brown on top.