In a large pot, bring water to boil. Boil the green beans for 3 to 5 minutes, until just tender. Drain and let cool.
In a large bowl, combine the cooled green beans with tomatoes and red onion. Toss to distribute evenly.
In a separate bowl, whisk together the dressing ingredients. Drizzle the dressing onto the salad, and toss to combine. At this point, you can cover the salad with plastic wrap and refrigerate. Add feta cheese just before serving.
Notes
Tip: soak the red onion in water for a few minutes to take out some of the strong onion flavor.
If you're counting WW Points be sure to use reduced fat feta cheese.