Prep the oven and pan: Preheat the oven to 400°F (200°C).
Line a large sheet pan with parchment for easy cleanup.
Season the zucchini: Toss the zucchini with 1.5 tablespoons olive oil, a pinch of salt, black pepper, and a few thyme leaves. Spread in an even layer on the sheet pan.
Start roasting the zucchini: Roast for 8–10 minutes to give it a head start. This helps it caramelize without overcooking the salmon.
Make the lemon-herb mixture: In a small bowl, whisk together the lemon zest, 1 tablespoon lemon juice, parsley, dill, remaining thyme, garlic, Dijon, remaining 1.5 tablespoons olive oil, and honey if using.
Add salt, pepper, and a pinch of red pepper flakes to taste.
Season the salmon: Pat the salmon dry. Sprinkle both sides with salt and pepper. If the fillets have skin, place them skin-side down on the sheet pan after the zucchini’s head start.
Add salmon to the pan: Remove the sheet pan from the oven.
Scoot the zucchini to make space, then nestle the salmon among the slices.
Spoon on the lemon-herb mix: Divide the mixture over the salmon fillets. Drizzle any extra over the zucchini. Add a few thin lemon slices on top if you like.
Roast to perfection: Return the pan to the oven and roast 8–12 minutes, depending on thickness.
The salmon should flake easily with a fork and look slightly translucent in the center. For thicker fillets, it may take up to 14 minutes.
Optional finish: For a light char, broil on high for 1–2 minutes at the end. Watch closely.
Rest and serve: Let the salmon rest 2 minutes.
Squeeze a final splash of lemon on top. Serve with the roasted zucchini and any pan juices.