Preheat your oven to 400°F (200°C) and line a large rimmed baking sheet with parchment paper for easy cleanup.
Cut the chicken breast into 1-inch bite-sized cubes and place them into a large mixing bowl.
Prepare the vegetables by cutting the broccoli into small florets, slicing the red bell pepper into thin strips, and peeling and cubing the sweet potato into 1/2-inch pieces.
Add all the prepared vegetables into the bowl with the chicken.
In a small bowl or jar, whisk together the olive oil, lemon juice, lemon zest, minced garlic, dried oregano, sea salt, and black pepper until well combined.
Pour the lemon-herb dressing over the chicken and vegetables, tossing thoroughly with your hands or a spatula to ensure every piece is evenly coated.
Spread the mixture in a single, even layer onto the prepared baking sheet, ensuring the pieces aren't too crowded so they roast rather than steam.
Place the sheet pan in the oven and roast for 20 to 25 minutes, or until the chicken is cooked through and the sweet potatoes are tender.
For extra color, you can broil the tray for the last 2 minutes until the edges of the broccoli are slightly charred.
Remove from the oven and serve immediately while hot and fragrant.