Place the chicken breast in a shallow dish and cover with buttermilk, marinating for at least 30 minutes in the refrigerator.
In a small bowl, whisk together the 3 tablespoons of whole wheat flour, sea salt, black pepper, garlic powder, and onion powder.
Remove the chicken from the buttermilk, allowing the excess to drip off, then dredge it thoroughly in the seasoned flour mixture.
Heat the avocado oil in a medium skillet over medium heat until shimmering.
Add the chicken to the skillet and cook for 5 to 7 minutes per side, or until the exterior is golden brown and the internal temperature reaches 165°F.
Remove the chicken from the pan and set it aside to rest on a plate.
In the same skillet, whisk together the milk, the remaining teaspoon of flour, and the dried thyme, scraping the bottom of the pan to release any flavorful browned bits.
Simmer the gravy for 2 to 3 minutes until it has thickened to a creamy consistency.
Pour the warm gravy over the chicken breast and serve immediately.