Make the dressing. Combine crème fraîche, Greek yogurt, lemon zest, lemon juice, horseradish, capers, dill, salt, and pepper.
Stir well and adjust seasoning. If you want it a little thinner, stir in a tiny bit of water. Set aside.
Prep the salmon: Preheat an oven to 350°F, place salmon on a parchment-lined baking sheet. Drizzle with olive oil, garlic, salt, pepper, and lemon zest.
Bake at 350°F for 15-17 minutes, then cool slightly.
Blanch the asparagus. Bring a pot of salted water to a rapid boil, add the asparagus, then cook for 3 minutes. Transfer immediately to an ice bath
Flake the cooled salmon into bite-size pieces.
In a large bowl, combine cooked barley, white beans, asparagus, and arugula. Toss with as much of the dressing as you want, then divide between plates and top with flaked salmon. Drizzle with olive oil, sprinkle with flaky sea salt, and garnish with fresh dill.