1. Preheat your oven to 400 F (200 C). Line a large baking sheet with parchment paper for easy cleanup.

2. Pat the chicken breasts dry with paper towels. Cut the chicken into 1-inch bite-sized pieces. In a medium bowl, toss the chicken pieces with 1 tablespoon of olive oil, Italian seasoning, garlic powder, salt, and black pepper until evenly coated.

3. In a separate large bowl, combine the broccoli florets, sliced red bell pepper, and sliced onion. Drizzle with the remaining 1 tablespoon of olive oil and toss until the vegetables are lightly coated.

4. Spread the seasoned chicken pieces in a single layer on one half of the prepared baking sheet. Arrange the seasoned vegetables in a single layer on the other half of the baking sheet. Ensure everything has a little space to roast evenly.

5. Place the baking sheet in the preheated oven and roast for 15-20 minutes. Halfway through the cooking time (around 10 minutes), carefully remove the baking sheet from the oven and give the chicken and vegetables a gentle stir or flip to ensure even cooking and browning. The chicken should be cooked through (internal temperature of 165 F or 74 C), and the vegetables should be tender-crisp and slightly charred at the edges.

6. Once cooked, remove the baking sheet from the oven. Serve the roasted chicken and vegetables immediately over a bed of cooked quinoa or brown rice. If desired, squeeze fresh lemon juice over the top for a bright finish.