Preheat your oven to 400°F (200°C) and line a large rimmed baking sheet with parchment paper for easy cleanup.
Dice the chicken breast, sweet potato, carrots, zucchini, and red bell pepper into uniform 1-inch pieces to ensure they cook evenly.
In a large mixing bowl, combine the diced chicken and all of the prepared vegetables.
Drizzle the avocado oil and lemon juice over the mixture, then sprinkle with sea salt, black pepper, garlic powder, and dried oregano.
Toss the ingredients thoroughly using your hands or large spoons until every piece is well-coated with the oil and seasonings.
Spread the mixture in a single, even layer on the baking sheet, making sure not to overcrowd the pan so the vegetables roast rather than steam.
Roast for 20 to 25 minutes, tossing the medley halfway through the cooking time, until the chicken is cooked through and the vegetables are tender with caramelized edges.