Preheat your oven to 400°F (200°C).
Toss the broccoli florets with half of the olive oil, salt, and pepper on a baking sheet.
Roast the broccoli for 15-20 minutes until the edges are slightly charred and tender.
In a small bowl, whisk together the remaining olive oil, lemon juice, and dried oregano.
Place the chicken breast in a shallow dish, coat with the lemon-herb mixture, and let marinate for at least 10 minutes.
Heat a grill pan or outdoor grill over medium-high heat and cook the chicken for 6-7 minutes per side, or until the internal temperature reaches 165°F.
While the chicken rests, ensure your quinoa is cooked and fluffy.
Slice the chicken into strips and serve alongside the quinoa and roasted broccoli.