You can use dry sherry in place of the mirin.
Whisk broth, mirin, soy sauce, and 1 tablespoon cornstarch together in bowl; set aside. Toss pork, 1 tablespoon oil, and remaining 2 tablespoons cornstarch together in large bowl. Heat 2 teaspoons oil in 12-inch nonstick skillet over medium-high heat until just smoking. Brown half of pork, 3 to 5 minutes; transfer to plate. Repeat with 2 teaspoons oil and remaining pork.
Add green beans and remaining 2 teaspoons oil to now-empty skillet and cook until bright green, about 1 minute. Add garlic and ginger and cook until fragrant, about 30 seconds. Whisk broth mixture to recombine and add to skillet. Cook until thickened, about 2 minutes. Return pork and any accumulated juices to skillet and cook until heated through, about 1 minute. Sprinkle with cashews and serve.
