How to Make It
To prepare pickles, place cucumbers in a wide shallow bowl. Combine water, vinegar, sugar, mustard seeds, and salt in a small saucepan over high heat; bring mixture to a boil. Remove from heat; carefully pour vinegar mixture over pickles. Let stand until ready to assemble sandwiches.
To prepare mayo, combine mayonnaise and next 7 ingredients (through garlic) in a medium bowl, stirring with a whisk. Refrigerate until ready to assemble sandwiches.
To prepare sandwiches, sprinkle chicken thighs evenly with salt, pepper, and onion powder. Combine buttermilk and egg in a large bowl, stirring with a whisk. Add chicken to bowl; toss to coat.
Pour oil to a depth of 1 inch in a large cast-iron skillet; heat oil to 325 °. Place flour in a shallow dish; dredge chicken thighs in flour, shaking off excess. Carefully add 4 chicken thighs to oil; cook 5 to 6 minutes on each side or until golden brown and done. Drain on a wire rack set over paper towels; keep warm. Repeat procedure with remaining chicken thighs.
To assemble sandwiches, drain pickles well; discard pickling liquid. Spread mayo evenly over bottom halves of buns; top evenly with pickles, lettuce, chicken thighs, and top halves of buns. Serve immediately.