In a large bowl, combine the cubed chicken, 2 tbsp olive oil, 1 tbsp lemon juice, oregano, garlic powder, 1/4 tsp salt, and 1/8 tsp pepper. Toss to coat evenly. Cover and refrigerate for at least 15 minutes, or up to 30 minutes.

Preheat your oven to 400°F (200°C). Line two large baking sheets with parchment paper for easier cleanup. Cook quinoa according to package directions: combine 1 cup quinoa with 2 cups water or broth in a saucepan. Bring to a boil, then reduce heat to low, cover, and simmer for 15 minutes, or until all liquid is absorbed. Let stand covered for 5 minutes, then fluff with a fork.

In another large bowl, combine the zucchini, red bell pepper, red onion, cherry tomatoes, and Kalamata olives. Drizzle with 2 tbsp olive oil, thyme, 1/2 tsp salt, and 1/4 tsp pepper. Toss until all vegetables are lightly coated.

Spread the seasoned vegetables in a single layer on one of the prepared baking sheets. Roast for 15 minutes.

While vegetables are roasting, spread the marinated chicken cubes in a single layer on the second prepared baking sheet. After the vegetables have roasted for 15 minutes, add the chicken baking sheet to the oven.

Continue roasting both the chicken and vegetables for another 15-20 minutes, or until the chicken is cooked through (internal temperature reaches 165°F/74°C) and the vegetables are tender-crisp and lightly caramelized. You may need to swap the baking sheets halfway through for even cooking.

While chicken and vegetables roast, whisk together the tahini, 2 tbsp lemon juice, minced garlic, 1/4 tsp salt, and a pinch of pepper in a small bowl. Gradually add water, 1 tablespoon at a time, whisking until the dressing reaches your desired creamy, pourable consistency.

Divide the cooked quinoa among four serving bowls. Top with equal portions of roasted chicken and roasted vegetables. Drizzle generously with the lemon-tahini dressing.

Garnish with fresh chopped parsley and crumbled feta cheese, if using. Serve warm.