Place the chicken breast between two sheets of parchment paper and pound to an even 1/2-inch thickness.
Submerge the chicken in buttermilk in a shallow bowl and let it marinate for at least 15 minutes to tenderize.
In a separate dish, whisk together the flour, garlic powder, onion powder, salt, pepper, and paprika.
Remove the chicken from the buttermilk and dredge it in the flour mixture, pressing firmly to ensure a thick coating on all sides.
Lightly brush or spray the coated chicken with avocado oil and place it in the air fryer basket.
Air-fry at 375°F for 12-15 minutes, flipping halfway through, until the exterior is golden and the internal temperature reaches 165°F.
Toast the sprouted grain bun until warm and slightly crunchy while the chicken rests.
Stir the Greek yogurt and Dijon mustard together in a small bowl to create a zesty spread.
Assemble the sandwich by spreading the sauce on the bun and layering with the crispy chicken, lettuce, tomato, and pickles.