Preheat your oven to 400°F and prepare a baking sheet with parchment paper.
In a small bowl, whisk together the lemon juice, garlic powder, and one teaspoon of olive oil to create a marinade.
Place the chicken breast in a shallow dish, coat with the marinade, and let it sit for 10 minutes.
Toss the broccoli florets with the remaining teaspoon of olive oil and a pinch of sea salt, then spread them in a single layer on the baking sheet.
Roast the broccoli for 15-20 minutes until the edges are tender and slightly charred.
While the broccoli roasts, heat a grill pan or outdoor grill to medium-high heat.
Grill the chicken breast for 6-7 minutes per side, or until the internal temperature reaches 165°F.
Allow the chicken to rest for 5 minutes before slicing it into strips.
Serve the sliced chicken over the warm cooked quinoa alongside the roasted broccoli.