In a small bowl, whisk together mayonnaise, ketchup, yellow mustard, garlic powder, and smoked paprika until smooth. Taste and adjust seasonings as needed. Refrigerate until ready to use. Pro tip: Make this sauce up to 3 days ahead for even better flavor development.

In a large mixing bowl, gently combine ground chicken, panko breadcrumbs, beaten egg, grated onion, minced garlic, mayonnaise, salt, pepper, paprika, onion powder, and cayenne if using. Mix just until ingredients are evenly distributed – don't overmix. Pro tip: Use your hands or a fork to mix gently. Overmixing will result in tough, dense patties.

Divide the mixture into 6 equal portions and gently shape into patties about 3/4 inch thick. Make a slight indent in the center of each patty with your thumb to prevent puffing during cooking. Pro tip: Wet your hands slightly when shaping to prevent sticking, and make patties slightly larger than your buns as they'll shrink during cooking.

Place shaped patties on a plate and refrigerate for at least 15 minutes. This helps them hold together better during cooking. Pro tip: For best results, chill for up to 2 hours. You can also freeze patties at this stage for up to 3 months.

Preheat your grill or grill pan to medium-high heat. Lightly oil the grates or pan to prevent sticking. Pro tip: Don't make the heat too high – chicken burgers need gentle cooking to stay juicy.

Cook patties for 5-6 minutes on the first side without pressing down. Flip carefully and cook for another 4-5 minutes until internal temperature reaches 165°F (74°C). Pro tip: Resist the urge to press down with your spatula – this squeezes out all the delicious juices.

If adding cheese, place slices on patties during the last minute of cooking and cover with a lid to help melt. Pro tip: A lid or piece of foil works great for creating a mini oven effect to melt the cheese perfectly.

While burgers cook, slice tomatoes and red onion. Wash and dry lettuce leaves thoroughly. Pro tip: Pat tomatoes dry with paper towels to prevent soggy buns.

Lightly toast burger buns on the grill or in a toaster until golden brown. Pro tip: Toasting the buns creates a barrier that helps prevent them from getting soggy from the burger juices.

Spread sauce on both halves of each toasted bun. On the bottom bun, layer lettuce, chicken patty with cheese, tomato slices, and red onion. Top with the other bun half. Pro tip: Let burgers rest for 2-3 minutes after cooking to allow juices to redistribute before serving.