Preheat your oven to 400°F (200°C) and line a baking sheet with parchment paper.
Toss the broccoli florets with half of the olive oil, a pinch of salt, and pepper, then spread them in a single layer on the baking sheet.
Roast the broccoli for 15-20 minutes until the edges are tender and slightly charred.
While the broccoli roasts, season the chicken breast with garlic powder, the remaining salt, pepper, and lemon juice.
Heat a grill pan or skillet over medium-high heat and lightly coat with the remaining olive oil.
Grill the chicken for 6-7 minutes per side, or until the internal temperature reaches 165°F (74°C).
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 quinoa, top with the sliced chicken, and serve alongside the roasted broccoli.