Bring a large pot of salted water to a boil. Add the green beans and cook for 3-4 minutes until bright green and tender-crisp. Drain and immediately transfer to a bowl of ice water to stop the cooking process. Let cool for about 5 minutes, then drain and pat dry.
In a small bowl, whisk together the olive oil, red wine vinegar, sumac, Dijon mustard, salt, and pepper until well combined.
In a large bowl, combine the cooled green beans and sliced shallots. Pour the dressing over the salad and toss gently to coat.
If using, sprinkle the toasted almonds and crumbled feta cheese on top before serving.
Serve immediately or refrigerate for up to 1 hour to allow the flavors to meld.