Preheat your oven to 400°F (200°C) and line a large rimmed baking sheet with parchment paper.
Slice the zucchini into half-moons, halve the champignon mushrooms, and cut the broccoli into small, bite-sized florets.
Cut the chicken breast into 1-inch cubes to ensure they cook at the same rate as the vegetables.
In a large mixing bowl, combine the chicken cubes, broccoli, zucchini, and mushrooms.
Drizzle with extra virgin olive oil and sprinkle with dried oregano, garlic powder, sea salt, and black pepper.
Toss everything thoroughly until the chicken and vegetables are evenly coated in oil and spices.
Spread the mixture in a single layer on the prepared baking sheet, making sure not to overcrowd the pan so the vegetables roast rather than steam.
Roast in the oven for 18 to 22 minutes, or until the chicken is cooked through and the vegetables are tender with golden-brown edges.
Remove from the oven and drizzle fresh lemon juice over the medley before serving warm.