In a large bowl, mix together ground chicken, soy sauce, sesame oil, garlic, lemongrass, and scallions. Divide the mixture into eight portions, pat into patties, and set aside. Place the grill pan over medium heat. Spread softened butter on hamburger buns and place them on a grill pan until light brown. Wipe the grill pan with a paper towel and brush it with vegetable oil. Place chicken patties on a grill pan and cook over medium-high heat, turning once, until the internal temperature reaches 165° F, about 7 minutes per side. During the last few minutes of cooking, baste each burger with hoisin sauce.

For Rainbow Sesame Slaw, in a medium bowl, combine all the vegetables. In a small bowl, stir together the vinegar, sugar, soy sauce, sesame oil, and sesame seeds. Pour this over the veggies and toss to combine.

For Sriracha Lime Mayo, stir all the ingredients together in a small bowl.

To assemble burgers, spread Sriracha Lime Mayo on each bottom and top bun. Place the chicken on the bun bottoms, add a heap of the Rainbow Sesame Slaw, and finish with the bun tops.