Prepare the chicken: Pound the chicken halves to an even 1/2-inch thickness.
Set up the breading station: In one shallow dish, mix flour, salt, pepper, paprika, and garlic powder. In a second dish, whisk the eggs and buttermilk together. In a third dish, place the panko breadcrumbs.
Dredge the chicken: Dip each chicken piece first into the flour mixture, shaking off excess. Then dip into the egg/buttermilk mixture. Finally, press firmly into the panko breadcrumbs to coat completely.
Make the sauce: Whisk together Dijon mustard, honey, mayonnaise, and apple cider vinegar until smooth. Set aside.
Cook the chicken: Heat about 1 inch of vegetable oil in a large skillet to 350°F (175°C). Carefully place the breaded chicken into the hot oil, ensuring not to overcrowd the pan. Fry for 4 to 6 minutes per side until golden brown and the internal temperature reaches 165°F (74°C).
Drain the chicken on a wire rack lined with paper towels. If using cheese, place a slice on the hot chicken immediately after removing it from the oil to melt.
Toast the buns lightly in the skillet or oven.
Assemble the burger: Spread a generous amount of honey mustard sauce on both halves of the bun. Place lettuce and tomato on the bottom bun. Top with the crispy chicken fillet, then place the top bun on.
Notes
For extra crispiness, chill the breaded chicken in the freezer for 15 minutes before frying.
Use panko breadcrumbs for the best crunchy texture.
If you prefer baking, spray the breaded chicken lightly with cooking spray and bake at 400°F (200°C) for 20-25 minutes, flipping halfway.