Searing green beans in a dry wok gives them a mild smoky flavor; you can get the same blistered effect with a large cast-iron skillet if you don't have a wok. The chiles in this recipe are sliced and cooked with their seeds — typically the hottest part of chiles — so keep that in mind when deciding how many to use.
Heat a wok over high heat until very hot. Add the beans and cook, stirring and tossing, until they begin to blister and brown in spots, 5-6 minutes. Add the garlic, chiles, and sesame seeds, and stir for 1 more minute. Add a few tablespoons of water, cover the wok, and cook until the beans are crisp-tender. Remove the cover and cook until dry. Remove from the heat and stir in the tamari.