Heat a cast iron skillet or wok, if you have one, over medium-high heat, then add 1-2 tablespoons of oil.
Add the green beans to the pan, stirring to coat evenly with oil. Cook, stirring frequently, until the beans begin to blister, about 10 minutes.
Turn the heat down to low and add the soy sauce, ponzu, water, sesame oil, sriracha, and garlic powder. Stir to coat all the green beans and cook about 3 minutes more.
Remove the green beans from the heat and place in a serving dish. Finish with lemon zest, a pinch of flaky salt, and a generous amount of sesame seeds.