Preheat your oven to 400°F (200°C) and line a large baking sheet with parchment paper.
Rinse the quinoa under cold water, then combine it with 0.5 cup of water in a small pot; bring to a boil, then cover and simmer for 15 minutes until fluffy.
Dice the chicken breast, zucchini, red bell pepper, and red onion into uniform bite-sized pieces.
Place the chicken and vegetables on the prepared baking sheet, then drizzle with 0.5 tablespoon of olive oil and sprinkle with half of the salt, pepper, garlic, and oregano.
Roast in the oven for 18 to 20 minutes until the chicken is cooked through and the vegetables are tender and slightly caramelized.
In a small bowl, whisk together the remaining 0.25 tablespoon of olive oil, lemon juice, salt, pepper, garlic, and oregano to create a bright dressing.
Combine the cooked quinoa and roasted mixture in a large bowl, pour the dressing over the top, and toss gently to combine before serving.