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 harissa paste, extra virgin olive oil, minced garlic, lemon juice, sea salt, and black pepper until well combined.
Cut the chicken breast into 1-inch cubes and slice the red bell pepper into thin strips.
Place the chicken cubes, broccoli florets, and bell pepper strips onto the prepared baking sheet.
Drizzle the spicy harissa mixture over the chicken and vegetables, tossing thoroughly with your hands or tongs to ensure every piece is coated.
Spread the ingredients out into a single layer, making sure not to overcrowd the pan so the vegetables roast rather than steam.
Bake for 18 to 22 minutes, or until the chicken is cooked through and the vegetables have developed slightly charred, caramelized edges.
Remove from the oven and serve immediately while hot, enjoying the bold and zesty Mediterranean flavors.