Preheat your oven to 400°F (200°C) and line a large sheet pan with parchment paper.
Dice the chicken breast into 1-inch cubes and chop the zucchini, bell pepper, and red onion into similar bite-sized pieces.
In a large bowl, whisk together the olive oil, lemon juice, minced garlic, dried oregano, sea salt, and black pepper.
Add the chicken and all vegetables to the bowl, tossing thoroughly until everything is evenly coated in the herb marinade.
Spread the mixture in a single layer on the prepared sheet pan, ensuring the ingredients are not overcrowded to allow for proper roasting.
Roast for 20-25 minutes, or until the chicken is cooked through and the vegetables are tender and slightly caramelized.
Remove from the oven and serve immediately, garnished with fresh herbs if desired.