Preheat your oven to 400 degrees Fahrenheit and line a large baking sheet with parchment paper for easy cleanup.
Cut the chicken breast into uniform bite-sized pieces and place them into a large mixing bowl.
Add the broccoli florets, chopped red bell pepper, and sliced red onion to the bowl with the chicken.
In a small bowl, whisk together the harissa paste and extra virgin olive oil until well combined.
Pour the harissa mixture over the chicken and vegetables, then sprinkle with sea salt and black pepper.
Toss everything thoroughly with your hands or a large spoon to ensure every piece is evenly coated in the marinade.
Spread the mixture in a single, even layer on the prepared baking sheet to ensure proper roasting.
Roast in the center of the oven for 18 to 20 minutes, or until the chicken is fully cooked and the vegetables are tender.
Remove from the oven and immediately drizzle with the fresh lemon juice to brighten the flavors.
Garnish with chopped fresh parsley and serve while hot.