In a shallow bowl, whisk together the buttermilk, sea salt, black pepper, paprika, and garlic powder.
Place the chicken breast in the buttermilk mixture and let it marinate for at least 15 minutes.
Prepare two separate shallow dishes: one with the whole wheat flour and the other with the panko breadcrumbs.
Remove the chicken from the buttermilk, dredge it lightly in the flour, dip it back into the buttermilk briefly, and then press it firmly into the panko until fully coated.
Lightly brush or spray the breaded chicken with avocado oil.
Place the chicken in an air fryer at 375°F (190°C) and cook for 12-15 minutes, flipping halfway through, until the internal temperature reaches 165°F and the exterior is golden brown.
During the last 2 minutes of cooking, place the split whole wheat bun in the air fryer to toast.
Assemble the sandwich by placing the butter lettuce on the bottom bun, followed by the crispy chicken and dill pickles, then top with the remaining bun half.