Preheat your oven to 400°F (200°C) and line a large sheet pan with parchment paper.
Chop the broccoli, red bell pepper, and zucchini into uniform bite-sized pieces to ensure even cooking.
Pat the chicken breast dry with a paper towel and slice it into even strips or cubes.
In a large mixing bowl, combine the chicken and vegetables with the olive oil, oregano, garlic powder, sea salt, and black pepper.
Toss the mixture thoroughly until everything is well coated in the oil and spices.
Spread the chicken and vegetables in a single layer on the prepared baking sheet, avoiding overcrowding.
Roast for 18 to 22 minutes, or until the chicken is cooked through and the vegetables are tender with slightly charred edges.
Remove from the oven, drizzle with fresh lemon juice, and serve immediately topped with the sliced avocado.