Heat large, deep skillet or wok 2 minutes over medium heat. Add oil, and swirl to coat pan. Increase heat to high, wait 30 seconds, then add green beans and big pinch of salt. Cook 3 minutes, shaking pan or using tongs to turn and move beans so they cook quickly and evenly. Stir in garlic and red pepper flakes, if desired, and cook 1 minute more, stirring constantly, or until beans are crisp-tender.