Preheat your oven to 400°F (200°C) and line a large baking sheet with parchment paper.
Chop the cauliflower into bite-sized florets, slice the zucchini into half-moons, and dice the red bell pepper into one-inch pieces.
In a small mixing bowl, whisk together the harissa paste, extra virgin olive oil, lemon juice, sea salt, and black pepper until well combined.
Place the chicken breast and all the chopped vegetables onto the prepared baking sheet.
Drizzle the harissa mixture over the chicken and vegetables, using your hands or a spatula to toss everything until thoroughly and evenly coated.
Spread the ingredients out in a single layer to ensure even roasting.
Bake for 20 to 25 minutes, or until the chicken reaches an internal temperature of 165°F and the vegetables are tender with slightly charred edges.
Remove from the oven and let the chicken rest for 5 minutes before slicing.
Garnish the entire dish with chopped fresh parsley and serve immediately.