Preheat your oven to 400°F (200°C) and line a large baking sheet with parchment paper.
Dice the chicken breast, zucchini, red bell pepper, and red onion into bite-sized, uniform pieces.
Place the chicken and vegetables on the prepared baking sheet, drizzle with olive oil, and sprinkle with sea salt, black pepper, garlic powder, and dried oregano.
Toss everything together until evenly coated, then spread into a single layer.
Roast in the oven for 18-20 minutes, or until the chicken is cooked through and the vegetables are tender and slightly caramelized.
While the vegetables roast, bring a pot of water to a boil and cook the buckwheat soba noodles according to package directions, usually about 4-5 minutes.
Drain the noodles and rinse briefly under warm water to prevent sticking.
In a large bowl, combine the cooked noodles with the roasted chicken and vegetables.
Drizzle with fresh lemon juice and toss gently to combine before serving warm.