Preheat your oven to 400°F (200°C) and line a large rimmed baking sheet with parchment paper for easy cleanup.
Peel the sweet potato and cut it into uniform 1/2-inch cubes to ensure even roasting.
In a small mixing bowl, whisk together the olive oil, lemon juice, lemon zest, dried oregano, garlic powder, sea salt, and black pepper to create the marinade.
Place the chicken breast and diced sweet potatoes on the prepared baking sheet, then drizzle with three-quarters of the lemon-herb mixture, tossing the potatoes to coat thoroughly.
Roast in the center of the oven for 15 minutes.
Remove the pan from the oven, add the broccoli florets to the empty spaces, and drizzle them with the remaining lemon-herb mixture.
Return the pan to the oven and roast for an additional 10 to 12 minutes, or until the chicken reaches an internal temperature of 165°F and the vegetables are tender and lightly browned.
Let the chicken rest for 5 minutes before slicing to keep it juicy, then serve alongside the roasted vegetables.