Combine butter, scallions, and lime zest in small bowl; set aside. Heat oil in 12-inch nonstick skillet over medium heat until just smoking. Add beans, 1/4 teaspoon salt, and 1/8 teaspoon pepper; cook, stirring occasionally, until spotty brown, 4 to 6 minutes. Add water, cover, and cook until beans are bright green and still crisp, about 2 minutes. Remove cover, increase heat to high, and cook until water evaporates, 30 to 60 seconds. Add butter mixture and continue to cook, stirring frequently, until beans are crisp-tender, lightly browned, and beginning to wrinkle, 1 to 3 minutes longer. Transfer green beans to serving bowl, toss with lime juice and tarragon; adjust seasoning with salt and pepper. Serve immediately.

Serves 4