Preheat your oven to 400°F (200°C) and line a large rimmed sheet pan with parchment paper for easy cleanup.
Prepare the Brussels sprouts by trimming the ends and slicing them in half, and cut the chicken breast into uniform 1-inch bite-sized pieces.
In a small glass bowl, whisk together the extra virgin olive oil, balsamic vinegar, maple syrup, minced garlic, sea salt, black pepper, and dried thyme until well combined.
Place the chicken pieces and halved Brussels sprouts onto the prepared sheet pan.
Drizzle the balsamic mixture over the ingredients and toss thoroughly with your hands or tongs to ensure every piece is well coated.
Arrange the ingredients in a single layer, making sure the Brussels sprouts are placed cut-side down to achieve maximum browning and crispiness.
Roast in the center of the oven for 20 to 25 minutes, tossing halfway through, until the chicken reaches an internal temperature of 165°F and the sprouts are tender with charred edges.