Preheat your oven to 400°F and line a baking sheet with parchment paper.
Toss the broccoli florets with half of the olive oil, a pinch of salt, and pepper, then roast for 15-20 minutes until the edges are slightly browned.
Rinse the quinoa under cold water and combine it with 1/2 cup of water in a small saucepan.
Bring the quinoa to a boil, then reduce heat to low, cover, and simmer for 12 minutes or until water is absorbed.
Season the chicken breast with garlic powder, salt, pepper, and the remaining olive oil.
Grill the chicken over medium-high heat for approximately 6-7 minutes per side until the internal temperature reaches 165°F.
Remove the chicken from the grill and let it rest for 5 minutes before slicing.
Fluff the cooked quinoa with a fork and stir in the fresh lemon juice.
Plate the sliced chicken over the lemon quinoa and serve with the roasted broccoli.