Prepare the Wasabi Ketchup

Begin by combining ketchup, soy sauce, and wasabi paste in a small bowl. Whisk the ingredients together until smooth, ensuring that the wasabi is evenly incorporated into the mixture.

Prepare the Burgers

Preheat your grill to medium heat. In a large mixing bowl, combine the panko breadcrumbs and milk, allowing them to rest for 2-3 minutes. Once softened, add the ground sirloin, ground pork, finely chopped onion, soy sauce, salt, and pepper. Knead the mixture until it becomes sticky and cohesive, then divide it into four equal portions.

Form the Patties

Lightly coat your hands with sesame oil to prevent sticking. Roll each portion of the meat into a ball, then gently flatten it with your palms, shaping it into a patty about ½ inch thick. Use the side of your hand to create a shallow indentation in the center of each patty to help maintain its shape while grilling.

Cook the Burgers

Place the patties on the grill, flipping them twice during cooking to ensure they are evenly browned and fully cooked through, with no pink in the center. This should take approximately 10 minutes. Alternatively, you may broil or sauté the burgers to your preference. After grilling, let the patties rest for 2 minutes before serving.