Preheat your oven to 400°F and prepare a baking sheet with parchment paper.
Toss the broccoli florets with half of the olive oil, salt, and pepper, then spread them in a single layer on the baking sheet.
Roast the broccoli for 15 to 20 minutes until the edges are tender and slightly charred.
While the broccoli roasts, whisk together the remaining olive oil, lemon juice, oregano, salt, and pepper in a small bowl.
Coat the chicken breast in the lemon-herb marinade and let it sit for 5 minutes.
Grill the chicken over medium-high heat for 6 to 7 minutes per side or until the internal temperature reaches 165°F.
Warm the pre-cooked quinoa in a small pan or microwave until fluffy.
Slice the grilled chicken and serve it over the quinoa with the roasted broccoli on the side.