Preheat oven to 375 degrees.
Bring a pot of water to a boil. Add in green beans, then lower heat. Cook for about 10 minutes.
In a separate pan, heat the garlic and coconut oil over medium heat. Add in the mushrooms and cook for about 5 minutes.
Add in the flour, then cook about 2 minutes. Next, mix the broth, milk, and cashew butter together. Add to the mushrooms and continue to cook until the sauce thickens. Remove from heat, add rosemary.
Place the green beans in a casserole dish. Top with the rosemary garlic mushrooms and mix in. Bake for 15 minutes.
Top the casserole with the crispy onions. Serve hot and enjoy!