Preheat your oven to 400°F and line a large rimmed baking sheet with parchment paper.
Peel the sweet potato and slice it into half-inch thick rounds, then toss them with half of the olive oil and a pinch of sea salt.
Arrange the sweet potato rounds in a single layer on the baking sheet and roast for 10 minutes.
While the potatoes roast, finely chop the fresh parsley and mix it in a small bowl with the garlic powder, sea salt, and black pepper.
Pat the salmon fillet dry with a paper towel, brush the top with Dijon mustard, and press the herb mixture firmly onto the mustard.
Remove the baking sheet from the oven, push the potatoes to one side, and place the salmon and broccoli florets on the other side.
Drizzle the broccoli with the remaining olive oil and lemon juice, then return the pan to the oven for 12 to 15 minutes until the salmon is flaky and the potatoes are tender.