Preheat the oven to 400°F and line a large sheet pan with parchment paper for easy cleanup.
Dice the chicken breast into 1-inch cubes and peel and chop the sweet potato into similar-sized pieces.
In a large bowl, combine the chicken, sweet potato, broccoli florets, sliced bell pepper, and red onion.
Whisk together the olive oil, lemon juice, oregano, garlic powder, sea salt, and black pepper in a small jar.
Pour the marinade over the chicken and vegetables, tossing well to ensure every piece is thoroughly coated.
Spread the mixture onto the prepared baking sheet in a single, even layer to ensure proper roasting.
Bake for 20 to 25 minutes, or until the chicken is golden and the sweet potatoes are tender when pierced with a fork.
Garnish with fresh chopped parsley and an extra squeeze of lemon if desired before serving.