Preheat your oven to 400°F and line a large baking sheet with parchment paper for easy cleanup.
Cut the chicken breast into 1-inch bite-sized cubes and place them in a medium mixing bowl.
Chop the zucchini, red bell pepper, and red onion into uniform pieces to ensure even roasting.
In a small bowl, whisk together the harissa paste, olive oil, lemon juice, garlic powder, sea salt, and black pepper.
Pour the harissa mixture over the chicken and vegetables, tossing thoroughly until every piece is coated in the spicy marinade.
Spread the mixture in a single layer on the prepared baking sheet, ensuring the pieces aren't overcrowded so they roast rather than steam.
Bake for 18-22 minutes until the chicken is cooked through and the vegetables have developed beautiful charred edges.
Remove from the oven and let rest for two minutes before serving to keep the chicken juicy.