Preheat your oven to 400°F and line a large rimmed baking sheet with parchment paper for easy cleanup.
Cut the chicken breast into uniform 1-inch bite-sized pieces to ensure they cook evenly with the vegetables.
Prepare the vegetables by chopping the cauliflower into small florets, slicing the carrots into rounds, and cutting the red onion into thin wedges.
Place the chicken, cauliflower, carrots, and onion onto the prepared baking sheet.
Drizzle the extra virgin olive oil over the mixture and sprinkle evenly with sea salt, black pepper, garlic powder, and dried oregano.
Toss everything together with your hands or tongs until the chicken and vegetables are thoroughly coated in oil and spices.
Spread the mixture out into a single layer, ensuring there is space between pieces so they roast rather than steam.
Bake for 20 to 25 minutes, tossing halfway through, until the chicken is cooked through and the vegetables are tender and golden brown.