Preheat and prep: Heat your oven to 400°F (200°C).
Line a large sheet pan with parchment for easier cleanup.
Toss the veggies: In a large bowl, combine broccoli, carrots, red bell pepper, and red onion. Drizzle with 2 tablespoons olive oil, and add ½ to ¾ teaspoon salt, black pepper to taste, and smoked paprika if using. Toss to coat and spread evenly on the sheet pan.
Start the roast: Roast the vegetables for 10 minutes to give them a head start.
This helps everything finish at the same time.
Make the garlic butter: In a small bowl, mix melted butter, minced garlic, lemon zest, and 1 tablespoon lemon juice. Add a pinch of red pepper flakes if you like a little kick.
Season the salmon: Pat the salmon dry with paper towels. Season both sides with the remaining salt and a few cracks of black pepper.
Add salmon to the pan: Pull the sheet pan from the oven.
Push the veggies to create four open spaces. Nestle the salmon fillets into those gaps, skin-side down if using skin-on pieces.
Brush and finish roasting: Spoon the garlic butter over the salmon. If using cherry tomatoes, scatter them around now.
Return the pan to the oven and roast for 10–12 minutes, depending on thickness.
Check doneness: The salmon should flake easily with a fork and be just opaque in the center. Internal temperature should read 125–130°F for medium and 140°F for well done, depending on preference.
Hit it with brightness: Squeeze the remaining lemon juice over the salmon and veggies. Sprinkle with chopped parsley or dill.
Serve: Plate the salmon with a generous scoop of roasted vegetables.
Add lemon wedges on the side. A drizzle of the pan juices makes it extra delicious.