Whisk together the buttermilk, beaten egg, ½ tsp salt, and ¼ tsp black pepper in a large bowl. Add the 4 chicken cutlets, submerge, cover, and refrigerate for at least 30 minutes.

Combine the flour, cornstarch, 1 tsp salt, ¾ tsp black pepper, garlic powder, onion powder, smoked paprika, cayenne, and oregano in a shallow dish and stir to combine.

Lift each cutlet from the buttermilk, let the excess drip off, press into the seasoned flour, dip back into the remaining buttermilk, and press into the flour again. Rest on a wire rack for 5 minutes.

Heat the oil in a heavy-bottomed pot to 350°F (175°C) and fry the cutlets 2 at a time for 5 to 6 minutes, flipping once, until deep golden and the internal temperature reads 165°F (74°C). Return oil to 350°F between batches.

Spread 1 tbsp mayonnaise on each top bun, layer ½ cup lettuce and 2 pickle slices on each bottom bun, top with a fried cutlet, and close the sandwich. Serve immediately.