Preheat your oven to 400°F (200°C) and line a large sheet pan with parchment paper.
Rinse the quinoa under cold water, then combine with 1 cup of water in a small saucepan; bring to a boil, then reduce heat to low, cover, and simmer for 15 minutes until fluffy.
In a small bowl, whisk together the extra virgin olive oil, the juice of half the lemon, minced garlic, dried oregano, sea salt, and black pepper.
Trim the woody ends off the asparagus and place them on one side of the sheet pan, then place the chicken breast on the other side.
Drizzle the lemon-herb oil mixture over both the chicken and the asparagus, tossing the vegetables to ensure they are evenly coated.
Slice the remaining half of the lemon into thin rounds and place them on top of the chicken and asparagus.
Roast in the oven for 20 to 25 minutes, or until the chicken reaches an internal temperature of 165°F and the asparagus is tender.
Fluff the cooked quinoa with a fork and serve the roasted chicken and asparagus over the grains, garnishing with freshly chopped parsley.