Preheat oven to 400°F (200°C) and line a large baking sheet with parchment paper.
Chop the bell peppers, zucchini, and red onion into bite-sized chunks.
In a large bowl, whisk together the harissa paste, olive oil, lemon juice, garlic powder, sea salt, and black pepper.
Cut the chicken breast into 1-inch cubes and toss them in the harissa marinade until thoroughly coated.
Add the chopped vegetables to the bowl and toss again to ensure everything is seasoned.
Spread the chicken and vegetables in a single layer on the prepared baking sheet.
Roast for 20-25 minutes, tossing halfway through, until the chicken is cooked through and the vegetables have a beautiful char.
Serve hot, perhaps with an extra squeeze of fresh lemon for brightness.