Preheat your oven to 400°F (200°C) and line a large rimmed baking sheet with parchment paper.
In a small bowl, whisk together the harissa paste, olive oil, lemon juice, minced garlic, sea salt, and black pepper to create the marinade.
Cut the chicken breast into 1-inch cubes and chop the bell pepper, red onion, and zucchini into bite-sized pieces.
Place the chicken and vegetables in a large mixing bowl, pour the harissa marinade over them, and toss until everything is thoroughly and evenly coated.
Spread the mixture in a single layer on the prepared baking sheet, ensuring there is space between the pieces for even roasting.
Roast for 20 to 25 minutes, or until the chicken is cooked through and the vegetables are tender and slightly charred at the edges.
Remove from the oven and garnish with freshly chopped parsley before serving hot.