Place the chicken breast between two sheets of parchment paper and pound with a meat mallet to an even thickness of about half an inch.
In a shallow bowl, whisk together the buttermilk, smoked paprika, garlic powder, sea salt, and black pepper.
Submerge the chicken in the buttermilk mixture and let it marinate for 15 minutes in the refrigerator.
Place the almond flour in a separate shallow dish and dredge the marinated chicken until it is thoroughly and evenly coated.
Lightly grease the air fryer basket with avocado oil, place the chicken inside, and spray the top of the chicken with the remaining oil.
Air fry at 375°F for 12 to 15 minutes, flipping the chicken halfway through, until the exterior is golden brown and crispy.
While the chicken cooks, mix the Greek yogurt and Dijon mustard in a small bowl to create a clean sandwich spread.
Toast the sprouted grain bun until warm and spread the yogurt-mustard mixture on both sides.
Assemble the sandwich by layering the crispy chicken, fresh arugula, and tomato slices onto the prepared bun.