Preheat your oven to 400°F and line a large rimmed baking sheet with parchment paper for easy cleanup.
Dice the chicken breast, sweet potato, and red bell pepper into uniform 1-inch cubes to ensure they cook at the same rate.
Trim the ends of the Brussels sprouts and slice them in half vertically.
Place the chicken and all the chopped vegetables onto the prepared baking sheet.
Drizzle the olive oil over the mixture and sprinkle evenly with garlic powder, dried oregano, sea salt, and black pepper.
Toss everything thoroughly with your hands or tongs until every piece is well-coated in oil and seasoning.
Spread the mixture out into a single layer, ensuring there is space between the items to allow for proper roasting and caramelization rather than steaming.
Bake for 20 to 25 minutes, tossing the medley halfway through, until the chicken reaches an internal temperature of 165°F and the sweet potatoes are fork-tender.
Remove from the oven and immediately give the pan a fresh squeeze of lemon juice to brighten the flavors.
Serve immediately or divide into airtight containers for a high-protein meal prep option throughout the week.