Bring a medium saucepan of heavily salted water to a boil over medium-high heat. Add the couscous and cook, stirring occasionally, until just tender, about 5 minutes.
Meanwhile, make the dressing: Place the dill, oil, vinegar, and shallots in a large bowl, season with salt and pepper, and whisk to combine; set aside.
When the couscous is ready, drain and rinse under cold water until cool. Drain again thoroughly.
Add the couscous, beans, cucumber, salt, and smoked salmon to the dressing and toss to combine. Taste and season with salt and pepper as needed. Let sit at least 15 minutes or refrigerate up to 1 day before serving.