Preheat your oven to 400°F (200°C) and line a large baking sheet with parchment paper for easy cleanup.
Peel the sweet potato and cut it into 1/2-inch cubes, then chop the broccoli into bite-sized florets and slice the bell pepper into strips.
Cut the chicken breast into even 1-inch strips to ensure they cook at the same rate as the vegetables.
In a large mixing bowl, whisk together the olive oil, lemon juice, dried oregano, garlic powder, sea salt, and black pepper.
Add the chicken, sweet potato cubes, broccoli, and peppers to the bowl and toss thoroughly until everything is evenly coated in the marinade.
Spread the mixture onto the prepared baking sheet in a single layer, ensuring the pieces are not overcrowded so they roast rather than steam.
Bake for 20 to 25 minutes, tossing halfway through, until the chicken reaches an internal temperature of 165°F and the sweet potatoes are tender and golden.