Preheat your oven to 400°F and line a baking sheet with parchment paper.
Toss the broccoli florets with half a tablespoon of 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, whisk together the lemon juice, minced garlic, another half tablespoon of olive oil, and a pinch of salt in a small bowl.
Coat the chicken breast in the lemon-garlic marinade and let it sit for at least 5 minutes.
Heat a grill pan or outdoor grill over medium-high heat and cook the chicken for 6-7 minutes per side until the internal temperature reaches 165°F.
Let the chicken rest for 3 minutes before slicing it into strips.
Fluff the cooked quinoa and stir in the remaining half tablespoon of olive oil and a pinch of salt.
Plate the quinoa topped with the sliced chicken and roasted broccoli, finishing with an extra squeeze of lemon if desired.