Preheat your oven to 400°F (200°C) and line a large rimmed baking sheet with parchment paper for easy cleanup.
Cut the chicken breast into uniform 1-inch bite-sized pieces and place them in a large mixing bowl.
Prepare the vegetables by chopping the zucchini into half-moons, breaking the broccoli into small florets, and slicing the mushrooms.
In a small jar or bowl, whisk together the extra virgin olive oil, minced garlic, dried oregano, sea salt, black pepper, and fresh lemon juice.
Pour the lemon-garlic dressing over the chicken and vegetables in the large bowl, tossing thoroughly to ensure every piece is well-coated.
Spread the mixture in a single, even layer on the prepared baking sheet, ensuring the pieces are not overcrowded to allow for proper roasting.
Roast in the center of the oven for 18 to 22 minutes, or until the chicken is cooked through and the vegetables are tender-crisp with golden, caramelized edges.