In a small bowl, whisk together the lemon juice, minced garlic, one tablespoon of olive oil, salt, pepper, and dried oregano to create the marinade.
Place the chicken breast in a shallow dish or reusable bag, coat with the marinade, and let it sit for at least 15 minutes.
Preheat your oven to 400°F and prepare a baking sheet with parchment paper.
Toss the broccoli florets with the remaining tablespoon of olive oil, salt, and pepper, then spread them in a single layer on the baking sheet.
Roast the broccoli for 15-20 minutes until the edges are charred and tender.
While the broccoli roasts, bring a half cup of water or vegetable broth to a boil in a small saucepan, add the quinoa, reduce to a simmer, cover, and cook for 15 minutes.
Heat a grill or grill pan over medium-high heat and cook the marinated chicken for 5-7 minutes per side until the internal temperature reaches 165°F.
Let the chicken rest for 5 minutes before slicing and serving alongside the fluffy quinoa and roasted broccoli.