Preheat your oven to 400°F (200°C) and line a large baking sheet with parchment paper.
Slice the chicken breast into even 1-inch strips to ensure uniform cooking.
In a small mixing bowl, whisk together the harissa paste, half of the olive oil, lemon juice, sea salt, and black pepper.
Place the chicken strips in a bowl and toss with the harissa mixture until every piece is thoroughly coated.
Slice the red bell pepper, zucchini, and red onion into bite-sized pieces.
Spread the vegetables onto the prepared baking sheet, drizzle with the remaining olive oil, and toss to coat.
Nestle the marinated chicken strips among the vegetables on the sheet pan.
Roast in the center of the oven for 18 to 22 minutes, or until the chicken is cooked through and the vegetables have developed charred, caramelized edges.
Remove from the oven and garnish with freshly chopped parsley before serving.