Preheat your oven to 400°F (200°C) and line a large baking sheet with parchment paper.
Cut the chicken breast into bite-sized 1-inch pieces and place them in a large mixing bowl along with the broccoli florets.
In a small jar or bowl, whisk together the olive oil, lemon juice, lemon zest, minced garlic, dried oregano, sea salt, and black pepper.
Pour the lemon-herb dressing over the chicken and broccoli, tossing thoroughly to ensure every piece is evenly coated.
Spread the mixture in a single layer on the prepared baking sheet, ensuring there is space between pieces for even roasting.
Bake for 18-20 minutes, or until the chicken is cooked through and the broccoli edges are slightly caramelized.
Warm the pre-cooked quinoa and serve the roasted chicken and broccoli directly over the grains.