Place the chicken breast between parchment paper and pound to an even 1/2-inch thickness.
Marinate the chicken in buttermilk for at least 20 minutes to tenderize.
In a shallow bowl, whisk together the whole wheat flour, garlic powder, onion powder, smoked paprika, sea salt, and black pepper.
Remove the chicken from the buttermilk, letting the excess drip off, then dredge thoroughly in the seasoned flour mixture.
Lightly coat the breaded chicken on all sides with the avocado oil using a brush or spray.
Place the chicken in an air fryer at 375°F for 12-15 minutes, flipping halfway through, until the exterior is golden and crispy.
Toast the whole wheat bun in a dry pan until warm and slightly browned.
Assemble the sandwich by placing the shredded romaine lettuce, the crispy chicken breast, and the dill pickles onto the toasted bun.