Brine: Place the evenly flattened chicken in a resealable bag or nonreactive container. Add the pickle juice, garlic powder, and paprika. Seal or cover and refrigerate for 4 to 8 hours, or overnight up to about 12 hours.

Dry: Remove the chicken and pat dry with paper towels. Discard the used brine.

Mix the coating: Combine the flour, paprika, garlic powder, onion powder, salt, black pepper, and optional cayenne in a shallow dish.

Mix the wet ingredients: Whisk the eggs and milk in a separate shallow dish.

Coat: Dip each piece of chicken into the egg mixture, let the excess drip off, then press into the seasoned flour. Repeat once for a thicker crust, if desired. Rest on a rack for 10 minutes while heating the oil.

Heat the oil: Add about 2 inches of oil to a heavy, deep pot or high-sided skillet, keeping it no more than halfway full. Heat to 350°F.

Fry: Cook in batches, approximately 4 to 6 minutes per side for ½-inch-thick chicken, until golden and the thickest part reaches 165°F. Adjust the heat as needed and let the oil return to 350°F between batches.

Drain: Transfer the cooked chicken to a separate clean wire rack and rest briefly while toasting the buns.

Toast: Toast the cut sides of the buns in a dry skillet until lightly golden.

Assemble: Divide the mayonnaise among the buns. Add lettuce, chicken, two pickle slices per sandwich, and optional tomato. Close the sandwiches and serve immediately.