Preheat your oven to 400°F and line a large rimmed baking sheet with parchment paper for easy cleanup.
Chop the red bell pepper, zucchini, and red onion into uniform, bite-sized pieces to ensure even roasting.
In a large mixing bowl, whisk together the harissa paste, extra virgin olive oil, lemon juice, sea salt, and black pepper until well combined.
Add the chicken breast and the chopped vegetables to the bowl, tossing thoroughly to ensure every piece is generously coated in the spicy marinade.
Spread the chicken and vegetable mixture in a single layer onto the prepared baking sheet, making sure not to overcrowd the pan so the vegetables roast rather than steam.
Place the sheet in the oven and roast for 20 to 25 minutes, or until the chicken reaches an internal temperature of 165°F and the vegetables are tender with slightly caramelized edges.
Remove from the oven, let the chicken rest for a few minutes, then garnish with freshly chopped parsley before serving.