Preheat the oven to 400°F (200°C). Position a rack in the middle so the salmon and asparagus roast evenly. A hot, dry oven gives the salmon a short blast of heat to set the exterior while keeping the interior moist.

Pat the salmon dry with paper towels and season both sides with a light pinch of salt and pepper. Drying the surface removes excess moisture so the fish browns slightly in the oven and the herb topping adheres.

Trim the asparagus: snap or cut off the woody ends (about the bottom 1–1½ inches). Place asparagus on a rimmed baking sheet large enough to hold the two fillets as well, so everything cooks in one pan for easy cleanup and flavor continuity.

In a small bowl, combine 3/4 of the lemon zest, 2 tablespoons lemon juice, minced garlic, chopped dill/parsley, 3/4 of the olive oil (about 3/4 Tbsp), 1/2 teaspoon salt and 1/4 teaspoon pepper. This lemon‑herb mixture will both flavor and protect the salmon during baking — the acid brightens the fish while oil helps conduct heat and carry flavor.

Brush the lemon‑herb mixture over the salmon, pressing lightly so some adheres to the surface. Place the fillets skin-side down on the baking sheet. Toss the asparagus with the remaining olive oil, a pinch of salt and pepper; spread in a single layer beside the salmon. Arranging them separately avoids steaming and ensures the asparagus roasts until slightly charred.

Roast in the preheated oven: bake for 10–14 minutes (about 10 minutes for thinner fillets, up to 14 minutes for thicker). Why this range? Salmon cooks quickly; you want an internal temperature of 120–125°F (49–52°C) for medium-rare or 130–135°F (54–57°C) for medium. Use an instant-read thermometer inserted into the thickest part to avoid overcooking — fish continues to carryover-cook after it comes out of the oven.

While the salmon and asparagus roast, warm the cooked brown rice: microwave covered for 60–90 seconds with a splash of water, or reheat in a small saucepan with 1–2 tablespoons water over medium-low heat, covered, stirring once, until steaming. Warming gently keeps the grains separate and avoids drying them out.

Remove the tray from the oven when salmon reaches desired doneness and asparagus is bright green with slight browning. Let the salmon rest 2 minutes — resting lets juices redistribute and prevents the flesh from looking dry when flaked.

Finish the plate: fluff the brown rice with a fork and divide between plates. Lay a salmon fillet over each mound, arrange asparagus alongside. Spoon any pan juices over the salmon. Finish with the remaining lemon zest, a squeeze of fresh lemon to taste, and a small pat of butter on each fillet if using — the butter adds a silky gloss and a touch of richness.

Garnish with extra chopped dill or parsley and freshly cracked black pepper. Serve immediately while hot, and encourage diners to squeeze more lemon if they prefer a brighter finish.