In a small bowl, combine olive oil (reserve 1.5 tbsp for roasting and 1 tbsp for the marinade), lemon juice, minced garlic, salt, and pepper to create the marinade.
Place the chicken breast in a shallow dish and pour the marinade over it, ensuring it is well-coated. Let it marinate in the refrigerator for at least 30 minutes.
Preheat your grill to medium-high heat. Grill the marinated chicken breast for about 6-7 minutes per side or until the internal temperature reaches 165°F.
While the chicken is grilling, preheat your oven to 425°F. Toss the broccoli with the reserved 1.5 tbsp olive oil, a pinch of salt, and pepper, then spread it out on a baking sheet.
Roast the broccoli in the oven for about 12-15 minutes, stirring halfway, until tender and slightly crispy.
Prepare the quinoa as per package instructions if not already cooked (for faster prep, you may cook it in advance) using a 1/3 cup serving.
Plate the grilled chicken alongside the cooked quinoa and roasted broccoli, and enjoy this balanced, flavorful lunch.