Place the chicken breast between two sheets of parchment paper and pound to an even half-inch thickness.
Place the chicken in a small bowl and pour the buttermilk over it, ensuring it is fully coated; marinate for 20 minutes.
In a shallow dish, whisk together the whole wheat flour, garlic powder, onion powder, paprika, sea salt, and black pepper.
Remove the chicken from the buttermilk, letting excess drip off, then dredge thoroughly in the flour mixture until coated.
Lightly spray the chicken on both sides with avocado oil and place in an air fryer basket.
Air fry at 375°F for 12-15 minutes, flipping halfway through, until the exterior is golden brown and the internal temperature reaches 165°F.
While the chicken cooks, mix the Greek yogurt and lemon juice in a small bowl to create a simple herb sauce.
Lightly toast the whole wheat bun, then assemble the sandwich with the yogurt sauce, lettuce, tomato, pickles, and the crispy chicken.