Preheat your oven to 400°F (200°C) and line a large sheet pan with parchment paper.
Peel the carrots and parsnips, then slice them into 1/2-inch thick rounds.
Place the sliced vegetables on the sheet pan and toss with olive oil, half of the sea salt, and half of the black pepper.
Roast the vegetables in the oven for 12 minutes to give them a head start.
While the vegetables roast, finely chop the parsley and dill.
In a small bowl, whisk together the Dijon mustard, lemon juice, chopped parsley, chopped dill, and garlic powder.
Remove the sheet pan from the oven and move the vegetables to the sides to make room in the center.
Pat the salmon fillet dry with a paper towel and place it in the center of the pan.
Spread the herb-mustard mixture evenly over the top of the salmon and season with the remaining salt and pepper.
Return the pan to the oven and roast for an additional 12-15 minutes, or until the salmon is opaque and flakes easily with a fork and the vegetables are golden and caramelized.