Blanch green beans and add to a large bowl. Toss with pomegranate seeds (to taste), chestnuts, and orange zest.
In a separate small bowl, add 2 tablespoons of fresh orange juice, diced shallot, red wine vinegar, and whole-grain mustard. Whisk ingredients together, then continue whisking while slowly adding olive oil until mixture is emulsified. Add more olive oil to taste to balance acidity.
Toss vinaigrette with bean mixture and season with salt and pepper to taste. Serve cold or at room temperature.