Preheat the oven to 400°F (200°C) and line a large baking sheet with parchment paper or foil.
Place the chicken breasts on the baking sheet, drizzle with olive oil, and season lightly with salt and pepper.
Arrange the sliced bell peppers, zucchini, red onion, and cherry tomatoes around the chicken in a single layer.
Drizzle the vegetables with olive oil and season with salt, pepper, and Italian seasoning.
In a small bowl, whisk together balsamic vinegar, honey or maple syrup, Dijon mustard (if using), and minced garlic until smooth.
Pour the balsamic glaze evenly over the chicken and vegetables.
Roast in the oven for 20 to 25 minutes.
Flip or stir the vegetables, drizzle any remaining glaze over the top, and roast for another 10 to 15 minutes until the chicken is cooked through and the vegetables are tender.
Remove from oven, let rest a few minutes, and serve warm with extra glaze if desired.