Bring a pot of salted water to a boil, add orzo and cook until al dente following package directions. While the pasta cooks, whisk together mayo, sour cream, Dijon mustard, olive oil, lemon juice, lemon zest, garlic powder and chopped dill in a small bowl.
When the orzo is tender, drain it in a colander and rinse under cool water until the pasta feels chilled. Shake off excess water, transfer the orzo to a large bowl, then chop cucumber and red onion, tear smoked salmon into bite-size pieces and add them along with capers.
Pour the dressing over the pasta mixture, season with salt and pepper, and toss gently until everything’s coated. Taste and adjust seasoning as needed, then cover and chill if you’d like before serving.