Preheat Oven & Prepare Pan: Adjust your oven rack to the middle position and preheat to 420°F (215°C). Line a large, rimmed baking sheet with parchment paper for easy cleanup, if desired.
Arrange Salmon: Pat the salmon filets dry with a paper towel. Place the salmon portions, skin-side down (if applicable), in the center of the prepared baking sheet, leaving space on the sides for the broccoli.
Prepare Broccoli: In a large mixing bowl, add the fresh broccoli florets.
Create Lemon-Butter Sauce: In a small bowl, whisk together the melted unsalted butter, olive oil, fresh lemon juice, minced garlic, lemon pepper seasoning, and optional red pepper flakes until well combined.
Season Components: Drizzle or spoon about half of the lemon-butter sauce evenly over the salmon filets. Pour the remaining sauce over the broccoli florets in the bowl and toss until the broccoli is thoroughly coated.
Assemble Sheet Pan: Arrange the seasoned broccoli florets in a single layer on the baking sheet around the salmon.
Roast to Perfection: Transfer the baking sheet to the preheated oven. Roast for 18-22 minutes, or until the salmon is cooked through and flakes easily with a fork, and the broccoli is tender-crisp with slightly browned edges. The internal temperature of the salmon should reach 135-145°F (57-63°C) for medium to well-done, depending on your preference.