Preheat your oven to 400°F (200°C) and line a large sheet pan with parchment paper for easy cleanup.
Prepare the vegetables by scrubbing the sweet potato and cutting it into 1-inch cubes, slicing the carrots into rounds, and breaking the broccoli into bite-sized florets.
In a large mixing bowl, whisk together the olive oil, lemon juice, dried oregano, garlic powder, sea salt, and black pepper to create the marinade.
Add the chicken breast and all the prepared vegetables to the bowl, tossing thoroughly until every piece is evenly coated in the herb mixture.
Spread the chicken and vegetables in a single layer on the prepared baking sheet, ensuring they are not overcrowded so they roast rather than steam.
Roast in the center of the oven for 20-25 minutes, or until the chicken reaches an internal temperature of 165°F and the sweet potatoes are fork-tender and golden.
Remove from the oven and let the chicken rest for 5 minutes before slicing to ensure it stays juicy, then plate alongside the roasted vegetables.