4 tablespoons olive oil, divided
1/4 cup finely chopped red onion
2 tablespoons red wine vinegar
1 1/2 teaspoons Dijon mustard
3/4 teaspoon fine salt, divided
1/4 teaspoon freshly ground black pepper
1 cup Israeli (pearl) couscous
2 cups water
4 ounces green beans, trimmed and cut into 1/2-inch pieces
4 ounces yellow wax beans, trimmed and cut into 1/2-inch pieces
1 (15-ounce) can kidney beans, drained and rinsed
2 tablespoons coarsely chopped fresh dill leaves
2 tablespoons coarsely chopped fresh Italian parsley leaves