Preheat your grill or grill pan to medium-high heat.
In a small bowl, combine olive oil, lemon juice, minced garlic, a pinch of salt, and black pepper to create the marinade.
Coat the chicken breast with the marinade and let it sit for at least 15 minutes to absorb the flavors.
While the chicken marinates, toss the broccoli with a drizzle of olive oil, salt, and pepper, then spread it out on a baking tray.
Roast the broccoli in a preheated oven at 425°F (220°C) for about 15-18 minutes until tender and slightly crispy on the edges.
Grill the marinated chicken breast for approximately 6-7 minutes per side, or until the internal temperature reaches 165°F (74°C).
Prepare the quinoa as per package instructions if not already cooked.
Plate the grilled chicken alongside the quinoa and roasted broccoli, then drizzle any extra pan juices over the top if desired.