Preheat your oven to 400°F and line a large rimmed baking sheet with parchment paper for easy cleanup.
In a small mixing bowl, whisk together the olive oil, harissa paste, honey, lemon juice, sea salt, and black pepper until well combined.
Cut the chicken breast into 1-inch cubes and chop the cauliflower, bell pepper, and red onion into similar bite-sized pieces.
Place the chicken and vegetables onto the prepared baking sheet and pour the harissa marinade over the top.
Toss everything thoroughly with your hands or tongs to ensure every piece is evenly coated in the spicy glaze.
Spread the mixture out into a single layer, ensuring there is space between the pieces to allow for proper roasting and caramelization.
Roast in the center of the oven for 20 to 25 minutes, or until the chicken is cooked through and the vegetables have developed charred, crispy edges.
Remove from the oven and sprinkle with freshly chopped parsley before serving hot.