Preheat your oven to 400°F and line a large sheet pan with parchment paper for easy cleanup.
Trim the ends of the Brussels sprouts and slice them in half; chop the red bell pepper into 1-inch bite-sized pieces.
Cut the chicken breast into 1-inch strips or cubes to ensure they cook at the same rate as the vegetables.
In a large mixing bowl, whisk together the olive oil, balsamic vinegar, dried oregano, garlic powder, sea salt, and black pepper.
Add the chicken, Brussels sprouts, and bell peppers to the bowl, tossing thoroughly until every piece is well-coated in the marinade.
Spread the mixture in a single, even layer on the prepared sheet pan, ensuring the chicken pieces are not touching for optimal browning.
Roast in the center of the oven for 20 to 25 minutes, flipping the ingredients halfway through, until the chicken is cooked through and the vegetables are caramelized.