Cook rinsed quinoa in water or broth according to its package, rest covered 5 minutes, fluff and spread on a shallow tray.
Heat oven to 400°F and arrange salmon skin-side down on one half of a lined sheet pan.
Mix 2 tablespoons oil, zest, 1 tablespoon lemon juice, garlic, dried dill, 1/2 teaspoon salt and 1/4 teaspoon pepper; season salmon and asparagus.
Roast 10 minutes, then check individually; remove salmon at 145°F and asparagus when crisp-tender, usually 11 to 16 minutes.
Whisk yogurt, fresh dill, Dijon, remaining lemon juice, oil, salt and pepper, then fold in dried cucumber.
Rest salmon 5 minutes, divide quinoa and asparagus among four containers, add salmon and pack sauce separately.