Preheat your oven to 400°F and line a large rimmed sheet pan with parchment paper for easy cleanup.
Cut the chicken breast into uniform 1-inch cubes and slice the bell pepper into thin strips.
Place the chicken cubes, broccoli florets, and bell pepper strips onto the prepared sheet pan.
In a small glass jar or bowl, whisk together the olive oil, lemon juice, lemon zest, oregano, garlic powder, sea salt, and black pepper.
Drizzle the lemon-herb dressing over the chicken and vegetables, then toss with your hands or tongs to ensure everything is thoroughly and evenly coated.
Spread the mixture out into a single layer across the pan, ensuring the chicken and veggies aren't overcrowded so they roast rather than steam.
Bake for 18 to 22 minutes, or until the chicken reaches an internal temperature of 165°F and the vegetables are tender with slightly charred edges.