Preheat your oven to 400°F (200°C) and line a large baking sheet with parchment paper.
Dice the Yukon Gold potato into small 1/2-inch cubes to ensure they cook quickly and evenly.
Toss the potato cubes with half of the olive oil, half of the sea salt, and half of the black pepper on the baking sheet.
Roast the potatoes in the preheated oven for 15 minutes.
While the potatoes roast, finely mince the fresh parsley and dill, then combine them in a small bowl with the Dijon mustard and lemon juice.
Pat the salmon fillet dry with a paper towel and spread the herb-mustard mixture evenly over the top of the fish.
Remove the baking sheet from the oven, push the potatoes to one side, and place the salmon and asparagus spears on the other side.
Drizzle the remaining olive oil, salt, and pepper over the asparagus spears.
Return the tray to the oven and roast for an additional 10 to 12 minutes, or until the salmon flakes easily with a fork and the potatoes are golden brown.
Serve immediately while hot, garnished with any remaining fresh herbs.