Preheat your oven to 400°F (200°C) and line a large sheet pan with parchment paper for easy cleanup.
Cut the chicken breast into uniform 1-inch cubes and place them in a large mixing bowl.
Chop the red bell pepper and red onion into 1-inch pieces, and break the broccoli into bite-sized florets, adding them to the bowl with the chicken.
In a small jar or bowl, whisk together the extra virgin olive oil, lemon juice, minced garlic, dried oregano, sea salt, and black pepper until well emulsified.
Pour the herb dressing over the chicken and vegetables, tossing thoroughly to ensure every piece is evenly coated.
Spread the mixture onto the prepared baking sheet in a single layer, ensuring there is enough space for the air to circulate so the vegetables roast rather than steam.
Roast in the center of the oven for 18 to 22 minutes, or until the chicken reaches an internal temperature of 165°F and the vegetables are tender and slightly charred at the edges.
Remove from the oven and let rest for 2 minutes before serving to allow the juices to redistribute.