Place the chicken breast between two pieces of parchment paper and pound to an even half-inch thickness.
In a small bowl, whisk together the Greek yogurt and lemon juice to create a thick buttermilk-style marinade.
In a separate shallow dish, combine the whole wheat flour, garlic powder, smoked paprika, sea salt, and black pepper.
Coat the chicken breast thoroughly in the yogurt mixture, then dredge in the seasoned flour until fully coated.
Lightly coat the chicken on both sides with avocado oil using a mister or brush.
Place the chicken in an air fryer at 375 degrees Fahrenheit for 12 to 15 minutes, flipping halfway through, until the exterior is golden and crispy.
Toast the whole grain bun lightly in a pan or toaster.
Assemble the sandwich by placing the crispy chicken on the bottom bun, followed by the pickles, tomato, and lettuce.