Pound the chicken pieces to an even thickness and season with salt and pepper.
Pour buttermilk into a shallow dish and dip each chicken piece to coat thoroughly, then let them sit while you prepare the coating.
In another shallow dish, mix the flour with a pinch of salt, and in a third dish, combine panko breadcrumbs.
Remove each piece of chicken from the buttermilk, letting excess drip off, then dredge first in the flour mixture, then in the buttermilk again, and finally coat evenly with panko breadcrumbs.
Heat vegetable oil in a large skillet over medium-high heat until it reaches about 350°F (175°C), or until a small piece of bread sizzles and bubbles.
Carefully place the coated chicken pieces into the hot oil and fry for about 4-5 minutes per side, until golden brown and crispy. Transfer to a paper-towel-lined plate to drain excess oil.
While the chicken fries, mix mayonnaise with sriracha to create a spicy mayo. Slice the pickles thinly and toast the sandwich buns lightly until golden.
Spread the spicy mayo generously on the bottom bun, then layer with sliced pickles and the hot, crispy fried chicken.
Top the sandwich with the other bun, gently pressing down to help everything stay together.
Slice the sandwich in half if desired, and serve immediately with extra pickles on the side for an extra tangy crunch.
