Preheat oven to 300 degrees F.
Stir together sriracha, tamari, and sesame oil. Toss walnuts with the mixture. Spread on baking sheet, and roast for 6-7 minutes, until fragrant. Remove walnuts from baking sheet and place on a plate until cool. Then finely chop.
Prepare an ice bath. Bring a large pot of water to boil, with 2 teaspoons of kosher salt. Add green beans, and cook for 3 minutes. Drain and immediately put green beans into ice bath. Once cool, remove green beans and lightly pat dry.
Heat a cast iron skillet to medium-high, and once it is very hot (you'll see a little smoke) add green beans, and let cook on each side until charred and blistered. You'll likely have to do this in two batches, as pan may not be big enough to put all in it at once.
Keep pan on the stove, but move to an area off the heat. Push green beans to the side of the skillet, and add olive oil to the other side. Add garlic and ginger, and let cook for one minute, then stir everything together.
Add tamari, vinegar, red pepper flakes, sesame seeds, and stir to coat. Toss with chopped sesame walnuts and serve.