Slice boneless, skinless chicken breasts into ½-inch thick fillets and set aside.

In a medium bowl, whisk together all-purpose flour, salt, black pepper, garlic powder, onion powder, paprika, and cayenne pepper to create the breading mix.

In another bowl, whisk a large egg, add a splash of water to create an egg wash.

Prepare a third bowl with breadcrumbs for breading the chicken.

Dredge each chicken fillet in the flour mix, dip in the egg wash, then coat with breadcrumbs.

Heat vegetable oil in a skillet until hot, about 350°F.

Fry the breaded chicken fillets for 4-5 minutes on each side until golden brown and crispy.

Lightly toast the hamburger buns in another pan until golden.

In a mixing bowl, combine mayonnaise, Dijon mustard, lemon juice, and lemon zest for the sauce.

Assemble the sandwich with sauce, chicken fillet, lettuce, tomato slices, and parsley.

Serve immediately with your favorite sides.