Preheat your oven to 400°F (200°C) and line a large baking sheet with parchment paper.
Chop the zucchini into half-moons and the red bell pepper into bite-sized pieces.
In a large bowl, toss the cauliflower florets, zucchini, and bell peppers with half of the olive oil, sea salt, and black pepper.
In a small bowl, whisk together the harissa paste, lemon juice, and the remaining olive oil to create a marinade.
Coat the chicken breast thoroughly with the harissa marinade and place it on the baking sheet.
Spread the seasoned vegetables around the chicken in a single layer to ensure even roasting.
Roast in the oven for 20 to 25 minutes, or until the chicken reaches an internal temperature of 165°F and the vegetables are tender and slightly charred.
Let the chicken rest for 5 minutes before slicing.
Plate the chicken and roasted vegetables, finishing each serving with a dollop of Greek yogurt to balance the spice.