Slice portobello mushrooms or use pre-sliced mushrooms.
Add 2 tablespoons of oil to the pan then add mushrooms to saute until tender and slightly reduced in size.
Once mushrooms have reduced in size add in 1-2 tablespoons of oil, or shortening, add 1/4 cup of all-purpose gluten-free flour, and coat the mushrooms.
It's okay if it's a bit dry, add in 1 cup of broth and stir until it begins to dissolve the flour, allow to simmer and thicken a bit.
Add 2 cups of coconut milk and mix until the sauce is creamy and thickened, and turn off the heat.
Add in optional garlic, Worcestershire sauce, salt and pepper if needed, and avocado oil mayo.
Add in strained anc cooked green beans and coat the beans.
Add mixture to large casserole dish and bake for 35 minutes.