Preheat your oven to 400°F and prepare a baking sheet with parchment paper.
In a small bowl, whisk together half of the olive oil, lemon juice, minced garlic, and dried oregano to create a marinade.
Place the chicken breast in a shallow dish, coat with the marinade, and let it sit for at least 10 minutes.
Toss the broccoli florets with the remaining olive oil and a pinch of salt, then spread them in a single layer on the baking sheet.
Roast the broccoli in the oven for 15-20 minutes until the edges are slightly charred and tender.
While the broccoli roasts, heat a grill pan or outdoor grill over medium-high heat.
Grill the chicken breast for 6-7 minutes per side or until the internal temperature reaches 165°F.
Let the chicken rest for 5 minutes before slicing it into strips.
Warm the pre-cooked quinoa if needed and fluff it with a fork.
Plate the fluffy quinoa alongside the roasted broccoli and top with the sliced grilled chicken.