Preheat oven to 400°F and line a large baking sheet with parchment paper.
Slice the chicken breast into 1-inch strips and place them in a large mixing bowl.
Chop the bell pepper, zucchini, and red onion into bite-sized pieces and add them to the bowl with the chicken.
Whisk together the harissa paste, olive oil, lemon juice, sea salt, black pepper, and garlic powder in a small ramekin.
Pour the harissa mixture over the chicken and vegetables, tossing thoroughly to ensure every piece is coated in the spicy glaze.
Spread the mixture in a single layer on the prepared baking sheet, ensuring nothing is overcrowded to allow for proper roasting.
Roast for 20-25 minutes, or until the chicken is cooked through and the vegetables have developed a slight char.
Serve immediately, drizzling any remaining pan juices over the top for extra flavor.