Preheat your oven to 400°F (200°C) and line a large baking sheet with parchment paper for easy cleanup.
Cut the chicken breast into bite-sized cubes and place them in a large mixing bowl.
Add the broccoli florets and sliced carrots to the bowl with the chicken.
In a small jar or bowl, whisk together the olive oil, lemon juice, dried oregano, garlic powder, sea salt, and black pepper.
Pour the marinade over the chicken and vegetables, tossing thoroughly to ensure every piece is evenly coated.
Spread the mixture in a single layer on the prepared baking sheet, ensuring nothing is overcrowded so the veggies roast rather than steam.
Bake for 20-25 minutes, or until the chicken is cooked through and the vegetables are tender-crisp with slightly browned edges.
Remove from the oven and serve immediately, perhaps with an extra squeeze of fresh lemon if desired.