Preheat your oven to 400°F and line a baking sheet with parchment paper.
Toss the broccoli florets with half of the olive oil and a pinch of salt, then spread them in a single layer on the baking sheet.
Roast the broccoli for 15 to 20 minutes until the edges are slightly browned and tender.
While the broccoli roasts, whisk together the remaining olive oil, lemon juice, garlic powder, salt, and pepper in a small bowl.
Brush the chicken breast with the lemon-garlic marinade and let it sit for 5 minutes.
Heat a grill pan or outdoor grill over medium-high heat and cook the chicken for 6 to 7 minutes per side, or until the internal temperature reaches 165°F.
Let the chicken rest for 3 minutes before slicing it into strips.
Fluff the pre-cooked quinoa and place it in a bowl, then top with the grilled chicken and roasted broccoli.
Garnish with an extra squeeze of fresh lemon if desired and serve immediately.