Preheat your oven to 400°F and line a large rimmed baking sheet with parchment paper for easy cleanup.
Slice the chicken breast into 1-inch cubes and chop the broccoli, bell pepper, and red onion into similar bite-sized pieces to ensure even cooking.
In a small glass jar or bowl, whisk together the extra virgin olive oil, fresh lemon juice, dried oregano, garlic powder, sea salt, and black pepper until emulsified.
Place the chicken and all the chopped vegetables onto the prepared baking sheet and pour the lemon-herb dressing over the top.
Use your hands or a spatula to toss everything together until every piece is well-coated, then spread them out into a single layer.
Roast for 20 to 25 minutes, tossing halfway through, until the chicken is golden and the vegetables are tender with slightly charred, crispy edges.