Preheat your oven to 400°F (200°C) and line a large rimmed baking sheet with parchment paper for easy cleanup.
In a small mixing bowl, whisk together the harissa paste, extra virgin olive oil, minced garlic, lemon juice, sea salt, and black pepper until well combined.
Cut the chicken breast into bite-sized cubes and slice the zucchini and red bell pepper into similar sized pieces.
Place the chicken cubes, cauliflower florets, zucchini, and bell peppers into a large bowl and pour the harissa marinade over the top.
Toss everything thoroughly with your hands or a spatula to ensure every piece of chicken and vegetable is evenly coated in the spice mixture.
Spread the mixture in a single, even layer on the prepared baking sheet, making sure not to overcrowd the pan so the vegetables roast and caramelize rather than steam.
Roast for 20 to 25 minutes, or until the chicken is cooked through and the vegetables are tender with slightly charred edges.
Remove from the oven and garnish with freshly chopped parsley before serving.