Place the chicken breast in a shallow bowl and cover with buttermilk; marinate for at least 20 minutes in the refrigerator.
In a separate small bowl, whisk together 2 tablespoons of arrowroot powder, garlic powder, onion powder, smoked paprika, sea salt, and black pepper.
Remove the chicken from the buttermilk, letting excess drip off, then dredge thoroughly in the arrowroot spice mixture until evenly coated.
Preheat your air fryer to 400°F and generously spray the chicken on both sides with avocado oil spray.
Air fry the chicken for 12-15 minutes, flipping halfway through, until the internal temperature reaches 165°F and the outside is golden brown.
While the chicken cooks, steam the green beans in a small amount of water until tender-crisp, about 5 minutes.
To make the gravy, whisk the remaining 1 tablespoon of arrowroot powder into the cold chicken bone broth in a small saucepan.
Bring the broth to a simmer over medium heat, whisking constantly until thickened, then stir in the almond milk and a pinch of extra pepper for creaminess.
Slice the crispy chicken and serve immediately drizzled with the warm gravy alongside the steamed green beans.