Preheat your oven to 400°F (200°C) and line a large sheet pan with parchment paper for easy cleanup.
Wash and dice the red potatoes into 1/2-inch cubes and slice the carrots into 1/4-inch thick rounds.
Place the potatoes and carrots on the sheet pan, drizzle with half of the olive oil, and sprinkle with half of the oregano, garlic powder, salt, and pepper.
Toss the vegetables to coat evenly and roast in the oven for 15 minutes.
While the vegetables roast, pat the salmon fillet dry with a paper towel and squeeze half of the lemon juice over the top.
Remove the pan from the oven and move the potatoes and carrots to one side. Place the salmon fillet and the broccoli florets on the other side.
Drizzle the remaining olive oil over the salmon and broccoli, then season everything with the remaining oregano, garlic powder, salt, and pepper.
Place the remaining lemon slices on top of the salmon and return the pan to the oven.
Roast for an additional 12 to 15 minutes, or until the salmon is flaky and the vegetables are tender and lightly browned.
Serve immediately while hot, ensuring you scrape any flavorful juices from the pan onto the salmon.