Preheat your oven to 400°F and line a large rimmed baking sheet with parchment paper for easy cleanup.
Peel the sweet potato and cut it into 1/2-inch cubes, then trim the ends of the brussels sprouts and slice them in half.
Cut the chicken breast into uniform 1-inch pieces to ensure even cooking across the sheet pan.
In a small glass bowl, whisk together the olive oil, maple syrup, Dijon mustard, sea salt, black pepper, and garlic powder until the glaze is emulsified.
Place the chicken, cubed sweet potatoes, and halved brussels sprouts onto the prepared baking sheet.
Drizzle the maple-mustard glaze over the chicken and vegetables, using your hands or a spatula to toss until every piece is well-coated.
Spread the ingredients out into a single layer, making sure the chicken and vegetables aren't crowded so they roast rather than steam.
Roast for 20 to 25 minutes, tossing the mixture halfway through, until the chicken is cooked through and the vegetables have developed beautiful caramelized edges.