Preheat oven to 400°F. Line a baking sheet with parchment paper.
In a large bowl, combine quinoa, bell peppers, tomatoes, and onion. Drizzle with olive oil and season with salt and pepper. Toss to combine.
Transfer the vegetables to the baking sheet and spread in an even layer. Roast in the preheated oven for 20 minutes, stirring halfway through.
In a small bowl, whisk together olive oil, lemon juice, garlic, oregano, and salt and pepper. Set aside.
In a large bowl, combine the roasted vegetables with the quinoa. Drizzle with the dressing and toss to combine.
Top with feta cheese and olives. Serve and enjoy!