Preheat your oven to 400°F and line a baking sheet with parchment paper.
In a small bowl, whisk together the lemon juice and minced garlic to create a simple marinade.
Place the chicken breast in a shallow dish, coat with the lemon-garlic mixture, and let it marinate for at least 10 minutes.
Toss the broccoli florets with olive oil and a pinch of sea salt on the prepared baking sheet.
Roast the broccoli in the oven for 15-20 minutes until the edges are tender and slightly browned.
While the broccoli roasts, heat a grill pan or outdoor grill over medium-high heat.
Grill the chicken breast for 6-7 minutes per side, or until the internal temperature reaches 165°F.
If your quinoa is not already cooked, prepare it according to package instructions while the chicken rests.
Slice the grilled chicken into strips and serve over the warm quinoa alongside the roasted broccoli.