Submerge the chicken fillets in pickle juice and refrigerate for 20 minutes to brine.
Whisk together flour, powdered sugar, smoked paprika, and garlic powder in a shallow dish.
Remove chicken from brine, press each fillet into the flour mixture to coat both sides, then shake off excess.
Heat peanut oil in a large skillet to 350°F / 175°C and fry the chicken for 3 to 4 minutes per side until golden and cooked to 165°F / 74°C.
Drain the chicken on a wire rack for 2 minutes to keep the coating crisp.
Place each fillet on a toasted brioche bun bottom, top with 4 pickle slices, and cover with the bun top.