1.Preheat oven to 375 degrees F, bring a large stockpot of water to a boil, and grease a large casserole dish with olive oil and then set aside.
2.Add the green beans to the boiling water and boil for 4-5 minutes, or until almost tender, but still slightly crisp. Drain the cooked green beans, then transfer to a bowl filled with ice water to stop them from cooking more. (This step is very important)
3.To make the crispy onion topping, start by heating olive oil in a large fry pan over medium-high heat until hot.
4.Add the thinly sliced onions and cook, stirring occasionally, for 5-8 minutes or until they are tender and starting to brown. Remove the onions and place into a medium mixing bowl and set aside.
5.In the same pan you used to cook the onions, add the almond meal. Cook, stirring very frequently, for 3-5 minutes, or until the almond meal is starts to turn lightly golden. Careful not to burn.
6.Remove from heat and transfer the toasted almond meal to the bowl with the onions. Stir in the 1/4 cup shredded parmesan cheese and salt, and then toss the mixture until combined. Set aside.
7.In the same pan, heat a little more olive oil until hot and add the mushrooms and cook for 4-5 minutes, or until they are tender, stirring occasionally.
8.Add the minced garlic and cook for an additional minute until fragrant, stirring frequently.
9.Sprinkle the chickpea flour (or almond flour) over the mushrooms, and stir to combine.
10. Slowly add the low sodium broth, whisking to combine until smooth.
11. Whisk in the almond milk, and bring the mixture to a simmer. Let cook for 2-3 minutes, or until thickened.
12. Stir in the remaining 1/3 cup parmesan cheese, salt, and pepper until the cheese is melted.
13. Transfer the cooked, chilled green beans into the pan with the mushroom sauce and toss until combined.
14. Pour the green bean mixture into the prepared baking dish and then top with the crispy onion topping evenly over the top.
15. Place in the oven, uncovered, and bake for 25-30 minutes, until the top is golden brown.