Preheat your oven to 400°F (200°C) and line a large rimmed baking sheet with parchment paper.
Cut the chicken breast into 1-inch cubes and place them into a large mixing bowl.
Chop the red bell pepper, zucchini, and red onion into bite-sized pieces and add them to the bowl with the chicken.
In a small bowl, whisk together the harissa paste, extra virgin olive oil, lemon juice, garlic powder, sea salt, and black pepper until smooth.
Pour the harissa mixture over the chicken and vegetables, tossing thoroughly to ensure every piece is well-coated in the spicy marinade.
Spread the mixture in a single layer across the prepared baking sheet, ensuring there is space between pieces for even roasting.
Roast in the oven for 18 to 22 minutes, or until the chicken is cooked through and the vegetables have developed slightly charred, caramelized edges.
Remove from the oven and garnish with freshly chopped cilantro before serving.