Preheat your grill or grill pan to medium-high heat.
In a small bowl, combine olive oil, lemon juice, garlic powder, salt, and pepper to create a marinade.
Coat the chicken breast evenly with the marinade and let it rest for 10 minutes.
While the chicken marinates, preheat the oven to 425°F for roasting the broccoli.
Toss the broccoli with a drizzle of olive oil, salt, and pepper, and spread it on a baking sheet.
Roast the broccoli in the oven for about 15-20 minutes, until tender and slightly charred.
Place the chicken on the grill and cook for about 6-7 minutes per side, or until the internal temperature reaches 165°F.
Warm the cooked quinoa if needed and plate it alongside the grilled chicken and roasted broccoli.
Finish with an extra squeeze of lemon juice over the chicken for added brightness before serving.