In a bowl, combine fish sauce and sugar. Marinate the steak for 15 minutes.
Meanwhile, combine dressing ingredients in another bowl.
Heat a cast-iron skillet or grill on medium-high heat. Pat the steak dry, drizzle a little oil in the pan or grill and sear on both sides until cooked to your liking. Allow to rest for 5 minutes. Slice into bite-sized pieces and toss in the dressing.
Toss the rest of the ingredients into a bowl, add to a plate, top with the steak and dressing, and sprinkle more mint and cilantro on top.