Preheat the oven to 200 degrees F. Pat salmon dry and season lightly with kosher salt and pepper.
Heat 1 tablespoon olive oil in an extra large skillet over medium heat. Add salmon in a single layer skin side up and sear 2–3 minutes, flip then cook a few more minutes until golden and barely cooked through. Transfer to a large plate and place into oven to keep warm.
Wipe skillet clean and remove any fish skin that stuck to it or use a clean skillet. Add remaining olive oil over medium heat and add asparagus. Season with salt and pepper. Cook 3–4 minutes until bright green and just tender. Transfer to plate with salmon.
In the same skillet, melt butter. Add shallot and whites of the scallions and cook 4-5 minutes until softened. Add garlic and cook 30 seconds.
Pour in half & half and bring to barely a simmer (do not boil). Add lemon zest. Simmer 3-4 minutes until slightly thickened. Season to taste.
Spoon sauce into a large serving bowl. Top with asparagus and salmon. Sprinkle with fresh dill, the greens of the scallions and sea salt. Serve with lemon wedges.