Preheat oven to 400 degrees F.
Wash and dry salmon fillets. Drizzle with oil and salt and pepper each side. Rub seasoning in and place on baking sheet. Bake for 10-13 minutes (depending on thickness of fillets).
In a medium bowl, toss asparagus with a drizzle of oil, and salt and pepper to taste—the stalks should be lightly oiled and not dry. Spread on sheet pan and create two spaces for salmon to sit. Place salmon on the pan, squeeze lemon over (straining any seeds out with your hand), and move to the oven. Bake salmon and asparagus for 10-13 minutes. Don’t overcook the salmon. Remember salmon will continue to cook slightly as it rests outside the oven.
While salmon and asparagus cook, sauté leeks in about 2 Tbsp of olive oil on medium-high heat. Cook until leeks begin to brown—5 minutes. Salt and pepper to taste, then add spinach. Stir until spinach wilts, then remove from heat.
When salmon and asparagus are done, remove form oven and allow to rest for a few minutes before plating and serving. If asparagus is thick, you may need to remove salmon and return to oven for an additional 5 minutes, if spears are too crunchy for your liking.
Plate by layering wilted greens, asparagus, and salmon fillet. Zest fresh lemon, and garnish with finely chopped dill.