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; place them on one side of the baking sheet.
In a small bowl, whisk together the olive oil, lemon juice, minced garlic, dried oregano, sea salt, and black pepper to create the zesty marinade.
Place the chicken breast in the center of the baking sheet and brush it generously with half of the lemon-herb mixture.
Toss the sweet potato cubes with half of the remaining marinade, then roast in the oven for 15 minutes.
Remove the sheet from the oven, add the broccoli florets to the remaining open space, and drizzle them with the rest of the marinade.
Return the pan to the oven and roast for an additional 10-12 minutes, or until the chicken reaches an internal temperature of 165°F and the vegetables are tender.
Let the chicken rest for 5 minutes before slicing to ensure it stays juicy, then serve alongside the roasted vegetables.