Preheat oven to 400°F (200°C) and line a large baking sheet with parchment paper.
In a large bowl, whisk together olive oil, lemon juice, dried oregano, dried thyme, garlic powder, salt, and black pepper.
Add the diced chicken breasts, broccoli florets, and sliced red bell pepper to the bowl. Toss well to coat everything evenly in the marinade.
Spread the chicken and vegetables in a single layer on the prepared baking sheet. Ensure there is space between ingredients so they roast properly.
Bake for 15-20 minutes, or until the chicken reaches an internal temperature of 165°F and the vegetables are tender.
Remove from oven, let rest for 3 minutes, and serve warm.