Preheat oven to 400°F (200°C) and line a large sheet pan with parchment paper.
Dice the chicken breast and sweet potato into 1-inch cubes to ensure even cooking.
Chop the broccoli into bite-sized florets and slice the bell pepper and onion into strips.
In a large bowl, whisk together avocado oil, lemon juice, oregano, garlic powder, salt, and pepper.
Add the chicken and vegetables to the bowl and toss until everything is thoroughly coated in the herb mixture.
Spread the mixture in a single layer on the prepared sheet pan, ensuring no overcrowding.
Roast for 20-25 minutes, tossing halfway through, until the chicken is cooked through and the sweet potatoes are tender.