For the vegetable and chicken quinoa bowls: Preheat the oven to 400 degrees F. In a large bowl, toss together the broccoli, squash, carrots and zucchini along with the garlic powder, 3 tablespoons olive oil, 1 teaspoon salt and 1/2 teaspoon black pepper. Pour the vegetables onto a large baking sheet, making sure they're in an even layer. Bake until the vegetables are softened and have a nice brown color to them, about 30 minutes.
Meanwhile, bring the chicken stock to a boil and add the quinoa. Cook, following the instructions on the quinoa package.
Sprinkle the chicken with additional salt and pepper. In a small skillet, brown the chicken in the remaining 2 teaspoons olive oil until cooked through. Set aside.
For the Greek vinaigrette: Add the olive oil, vinegar, oregano, 1 teaspoon salt and 1/2 teaspoon pepper to a small mason jar. Tightly close the lid, and shake!
To assemble the bowls: Evenly distribute the quinoa into 2 bowls, then evenly distribute the vegetables and chicken into each bowl. Drizzle the dressing on top.