Place the chicken breast in a shallow bowl and pour the buttermilk over it, ensuring it is fully submerged; let it marinate for at least 20 minutes.
In a separate shallow dish, whisk together the whole wheat flour, garlic powder, onion powder, smoked paprika, sea salt, and black pepper.
Remove the chicken from the buttermilk, allowing the excess to drip off, then dredge it thoroughly in the flour mixture until well-coated.
Heat the avocado oil in a cast-iron skillet over medium heat until shimmering.
Place the chicken in the skillet and cook for 5-6 minutes per side until the crust is golden brown and the internal temperature reaches 165°F.
Remove the chicken from the pan and set aside to rest on a wire rack.
In the same skillet, whisk the arrowroot starch into the almond milk until smooth, then pour the mixture into the pan drippings.
Simmer the gravy over low heat, whisking constantly, until thickened; stir in the fresh thyme.
Serve the crispy chicken drizzled generously with the warm herb gravy.