Preheat your oven to 400°F and line a large baking sheet with parchment paper.
In a small bowl, whisk together the olive oil, lemon juice, lemon zest, dried oregano, garlic powder, sea salt, and black pepper to create the marinade.
Place the chicken breasts on one side of the prepared baking sheet and brush them generously with two-thirds of the lemon-herb mixture.
Roast the chicken in the oven for 10 minutes.
Remove the pan and add the asparagus spears to the empty side, drizzling them with the remaining lemon-herb mixture and tossing to coat well.
Return the pan to the oven and roast for an additional 10-12 minutes, or until the chicken reaches an internal temperature of 165°F and the asparagus is crisp-tender.
Let the chicken rest for 5 minutes before slicing to ensure it stays juicy and tender.