Bring 8 cups water to a boil in a Dutch oven. Add green beans, and cook 4 minutes or until crisp-tender.
. While beans are cooking, heat oil in a small saucepan over medium heat. Add garlic; sauté 3 minutes or until lightly browned. Remove from heat; add vinegar, mustard, and salt, stirring well with a whisk.
. Drain beans, and return to pan. Pour vinaigrette over beans; toss gently to coat. Sprinkle with feta cheese. Serve immediately.