In a small bowl, whisk together the lemon juice, half of the olive oil, and minced garlic to create a marinade.
Place the chicken breast in a shallow dish, coat with the marinade, and let sit for at least 15 minutes.
Preheat your oven to 400°F and line a baking sheet with parchment paper.
Toss the broccoli florets with the remaining olive oil, 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 slightly charred and tender.
While the broccoli roasts, preheat a grill or grill pan over medium-high heat.
Grill the chicken 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.
Fluff the pre-cooked quinoa with a fork and place it in a bowl.
Top the quinoa with the sliced grilled chicken and the roasted broccoli florets.