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

2. Cut the boneless, skinless chicken breasts into roughly 1-inch pieces. Do the same for the broccoli florets, red and orange bell peppers, and red onion wedges. Aim for pieces of similar size to ensure even cooking. Place all the chopped chicken and vegetables onto the prepared baking sheet.

3. In a small bowl, whisk together the olive oil, balsamic vinegar, honey, Dijon mustard, minced garlic, dried oregano, salt, and black pepper until well combined. This creates the flavorful coating for your chicken and vegetables.

4. Pour the balsamic mixture over the chicken and vegetables on the baking sheet. Use your hands or a large spoon to toss everything together, ensuring all the chicken and vegetables are thoroughly coated in the delicious glaze. Spread them out into a single layer on the baking sheet; avoid overcrowding to ensure they roast rather than steam.

5. Place the baking sheet in the preheated oven and roast for 20-25 minutes. About halfway through (around 10-12 minutes), give the ingredients a good stir to promote even cooking and caramelization. The chicken should be cooked through (no longer pink inside, reaching an internal temperature of 165 F or 74 C), and the vegetables should be tender-crisp with slightly browned edges.

6. Once cooked, remove the baking sheet from the oven. If desired, sprinkle with fresh chopped parsley for a pop of color and freshness. Serve immediately and enjoy your easy, flavorful one-pan meal!