Preheat your oven to 400°F (200°C) and prepare a baking sheet with parchment paper.
Toss the broccoli florets with one teaspoon of olive oil, salt, and pepper, then spread them on the baking sheet.
Roast the broccoli for 15-20 minutes until the edges are tender and slightly charred.
In a small bowl, whisk together the remaining teaspoon of olive oil, lemon juice, dried oregano, and a pinch of salt.
Place the chicken breast in a shallow dish, coat thoroughly with the lemon-herb marinade, and let it sit for 10 minutes.
Heat a grill pan or outdoor grill over medium-high heat and lightly oil the grates.
Grill the chicken for 5-7 minutes per side, or until the internal temperature reaches 165°F (74°C).
Warm the pre-cooked quinoa and fluff it with a fork before placing it on a plate.
Slice the grilled chicken and serve it alongside the quinoa and roasted broccoli.