1/3 cup tamari or soy sauce
2 tablespoons brown sugar
1 tablespoon finely grated peeled fresh ginger
1 tablespoon Asian fish sauce
1   stalk lemongrass, inner core only, finely minced
    grated zest of 1 lime
2 tablespoons peanut oil
1/4 teaspoon red pepper flakes, or more to taste
12 ounces sirloin strip steak, trimmed of fat and cut into thin (1/8 inch) strips
6 ounces fresh green beans, trimmed, cooked until just crisp tender
2 tablespoons snipped chives
1 cup chopped cocktail peanuts