"These are great chicken burgers made with ground chicken and blue cheese. They are served on a toasted bun with a mayo and Dijon sauce. Everyone loved them! I have served the leftovers the next day and they taste almost as good."
Whisk mayonnaise and Dijon mustard together in a small bowl. Transfer to the refrigerator.
Mix chicken, panko bread crumbs, milk, onion, celery, blue cheese, garlic powder, salt, and pepper together in a large bowl. Shape into 4 patties.
Heat olive oil in a large skillet over medium heat. Cook patties until browned and the juices run clear, 5 to 7 minutes per side. An instant-read thermometer inserted into the center should read at least 165 degrees F (74 degrees C).
Spread mayonnaise mixture over both sides of each bun. Place a cooked patty, 1 tomato slice, and 1 lettuce leaf in each bun.