Preheat your oven to 400°F (200°C) and line a large sheet pan with parchment paper for easy cleanup.
Pat the chicken breast dry with a paper towel and cut it into even, bite-sized cubes to ensure uniform cooking.
Prepare the vegetables by halving the Brussels sprouts, slicing the carrots into rounds, and chopping the bell pepper into one-inch pieces.
In a large mixing bowl, combine the chicken, vegetables, olive oil, minced garlic, rosemary, thyme, salt, and pepper, tossing thoroughly to coat every piece.
Spread the mixture in a single layer on the prepared baking sheet, ensuring the ingredients are not overcrowded so they roast rather than steam.
Roast for 20 to 25 minutes, tossing the ingredients halfway through, until the chicken is cooked through and the vegetables are golden and tender.
Remove from the oven and serve immediately while the herbs are fragrant and the chicken is juicy.