Preheat your oven to 400°F (200°C) and line a large baking sheet with parchment paper for easy cleanup.
Dice the zucchini, red bell pepper, red onion, and sweet potato into uniform 1-inch pieces to ensure even cooking.
In a small bowl, whisk together the olive oil, lemon juice, minced garlic, dried oregano, sea salt, and black pepper.
Place the chicken breast and chopped vegetables on the prepared baking sheet, then drizzle the lemon-herb mixture over everything, tossing well to coat.
Arrange the chicken in the center and spread the vegetables in a single layer around it.
Roast for 20-25 minutes, or until the chicken reaches an internal temperature of 165°F and the vegetables are tender and slightly caramelized.
Let the chicken rest for 5 minutes before slicing and serving alongside the roasted vegetable medley.