Line a baking sheet with tin foil then top with two cooling racks.
Cut the chicken breasts in half lengthwise then cut each piece into half widthwise. You should end up with four pieces of the same thickness. Season both sides of the meat with sea salt, freshly cracked pepper, and garlic powder, to taste. Pour the flour onto a flat plate. Whisk the egg and milk together in a bowl. Pour the panko onto a flat plate.
Dredge the chicken into the flour; next dip into the egg mixture followed by dipping into the panko crumbs, making sure to get an even coating. Place onto the cooling racks; repeat with the remaining chicken. Place the chicken into the refrigerator for 30 minutes. Side Note: Don't skip this step, it helps the panko adhere to the chicken.
After the chicken has been in the refrigerator for 30 minutes, remove and set it on the counter for 15 minutes. Heat half of the oil into a large skillet over medium-high heat. Once the pan is hot, add four pieces of the panko-crusted chicken and cook for 4-5 minutes on the first side, until golden brown. Flip the chicken over and cook for another 3 minutes or until the chicken is golden brown and cooked through. Remove from the skillet and place on a plate with a tin foil tent. Repeat the process with the remaining oil and chicken.
Place the coleslaw mix, green onions, and cilantro in a bowl. In another bowl, combine the grated ginger, soy sauce, lime juice, and rice vinegar. Whisk the ingredients while adding the sesame oil into the dressing. Pour the dressing over the coleslaw mixture and toss to coat. Sprinkle with sesame seeds if desired. Side Note: I made the coleslaw when I started cooking the chicken so it would not get soggy.
Combine the mayonnaise together with the sriracha sauce, to taste. We liked our sauce spicy. Set aside.
Toast your hamburger buns in the oven for a few minutes, if you prefer. Slather some sriracha mayonnaise on the bun, place a piece of chicken on top then a good spoonful of slaw. Slather the top bun with more sriracha mayonnaise, if desired. Serve immediately. Enjoy!