Preheat your oven to 400°F (200°C) and line a large baking sheet with parchment paper to prevent sticking.
Cut the chicken breast into 1-inch cubes and chop the sweet potato, broccoli, and red bell pepper into uniform, bite-sized pieces.
In a small mixing bowl, whisk together the olive oil, lemon juice, dried oregano, garlic powder, sea salt, and black pepper until well combined.
Place the chicken and all the vegetables onto the prepared baking sheet, then pour the lemon-herb marinade over the top.
Toss the ingredients thoroughly with your hands or tongs to ensure every piece is evenly coated in the marinade.
Spread everything out into a single layer, ensuring the chicken and vegetables aren't overcrowded so they roast rather than steam.
Bake for 20 to 25 minutes, or until the chicken reaches an internal temperature of 165°F and the sweet potatoes are fork-tender.