In a small bowl, whisk together the red wine vinegar, olive oil, red onion, salt, sugar and pepper until combined. Allow the mixture to sit at room temperature while you prepare the rest of the ingredients. This will allow the vinegar to soften the harsh flavors of the red onion.

Fill a large pot halfway with water and place over high heat. While you are waiting for the water to boil, fill a large bowl half full of ice water and set aside. When the water boils, add the green beans. Allow the green beans to cook until they are crisp-tender (or however you like them best), about 1–2 minutes. Drain the green beans and immediately submerge them in the ice water to stop the cooking. Once the beans are cold, drain them again and pat dry with paper towels.

Place the green beans, grape tomatoes and red wine vinaigrette into a large mixing bowl and toss gently to coat the vegetables in the dressing. Cover with plastic wrap and refrigerate for a minimum of 1 hour.

Remove from the refrigerator and toss once again to coat the vegetables in the dressing. Sprinkle feta cheese crumbles over the top of the salad and serve nice and cold. Enjoy!