Preheat your oven to 400°F (200°C) and line a large rimmed baking sheet with parchment paper for easy cleanup.
Rinse the quinoa in a fine-mesh strainer under cold water, then combine it with 0.5 cup 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 mixing bowl, whisk together 0.5 tbsp of the olive oil, lemon juice, lemon zest, minced garlic, chopped rosemary, sea salt, and black pepper to create the marinade.
Place the chicken breast, broccoli florets, and trimmed asparagus spears on the prepared baking sheet.
Drizzle the remaining 0.5 tbsp of olive oil over the vegetables and pour the lemon-herb marinade over the chicken, tossing the vegetables slightly to ensure they are evenly coated.
Roast in the center of the oven for 18 to 22 minutes, or until the chicken reaches an internal temperature of 165°F and the vegetables are tender with slightly charred edges.
Remove from the oven and let the chicken rest for 5 minutes before slicing it against the grain.
Serve the sliced chicken and roasted vegetables over the cooked quinoa, drizzling any remaining juices from the pan over the top.