Preheat your oven to 425°F (220°C) and line a large rimmed baking sheet with parchment paper for easy cleanup.
Pat the chicken legs thoroughly dry with paper towels to ensure the skin achieves maximum crispiness during roasting.
In a small bowl, whisk together the olive oil, dried rosemary, dried thyme, garlic powder, sea salt, and black pepper.
Rub the herb oil mixture generously over the chicken legs, ensuring you coat all sides and even under the skin if possible.
Place the chicken legs on the prepared baking sheet and roast for 20 minutes.
While the chicken is roasting, trim the woody ends off the asparagus spears.
Remove the baking sheet from the oven and arrange the asparagus in a single layer in the remaining space, tossing them lightly in the rendered chicken fat.
Return the tray to the oven and continue roasting for another 15 to 20 minutes, or until the chicken reaches an internal temperature of 165°F.
Remove from the oven and squeeze the fresh lemon juice over the chicken and asparagus before serving hot.