Preheat your oven to 400 degrees Fahrenheit and line a large baking sheet with parchment paper.
Peel and dice the sweet potato into half-inch cubes, and chop the broccoli, bell pepper, and red onion into similar bite-sized pieces.
Cut the chicken breast into one-inch cubes, ensuring they are uniform in size for even cooking.
Spread the chicken and all the chopped vegetables across the prepared baking sheet in a single layer.
Drizzle the extra virgin olive oil over the chicken and vegetables, then sprinkle evenly with sea salt, black pepper, garlic powder, and dried oregano.
Use your hands or a spatula to toss everything together until every piece is well-coated with oil and spices.
Roast in the oven for 25 to 30 minutes, or until the chicken is cooked through and the sweet potatoes are fork-tender.
While the medley roasts, warm the cooked quinoa in a small saucepan or microwave.
Divide the quinoa into bowls, top with the roasted chicken and vegetable mixture, and finish with sliced avocado and a bright squeeze of lemon juice.