Place the chicken breast in a shallow bowl and pour the buttermilk over it, ensuring it is fully submerged; marinate for 20-30 minutes.
In a separate small bowl, whisk together the almond flour, sea salt, black pepper, garlic powder, and onion powder.
Remove the chicken from the buttermilk, letting the excess drip off, and dredge it thoroughly in the seasoned almond flour mixture.
Lightly coat the chicken with avocado oil and place it in the air fryer basket.
Air fry at 375°F for 15-18 minutes, flipping halfway through, until the exterior is golden and the internal temperature reaches 165°F.
While the chicken cooks, steam the green beans until tender-crisp, about 5-6 minutes.
In a small saucepan over medium heat, whisk the almond milk and arrowroot powder together until the mixture simmers and thickens into a smooth gravy.
Serve the crispy chicken topped with the warm gravy alongside the steamed green beans.