Preheat your grill or grill pan over medium-high heat.
In a small bowl, combine the lemon juice, minced garlic, salt, and black pepper.
Brush the chicken breast with the mixture, ensuring an even coating.
Grill the chicken for about 6-7 minutes on each side or until fully cooked and juices run clear.
While the chicken grills, preheat your oven to 425°F for the broccoli.
Toss the broccoli florets with olive oil, salt, and pepper, and spread them on a baking sheet.
Roast the broccoli in the preheated oven for about 15 minutes, until tender and slightly charred.
Prepare the quinoa according to package instructions if not pre-cooked.
Plate the dish by layering the quinoa with the roasted broccoli and topping with the grilled chicken breast.
Drizzle additional lemon juice over the chicken, if desired, and serve warm.