Preheat your oven to 425°F.
In a small bowl, combine lemon juice, minced garlic, salt, and pepper to taste. Use half of this mixture to marinate the chicken breast for about 15 minutes.
Slice the bell pepper, zucchini, and red onion into bite-sized pieces and toss them with olive oil, the remaining lemon-garlic mixture, and a pinch of salt.
Place the marinated chicken breast on a baking tray and arrange the vegetables around it.
Roast in the oven for 20-25 minutes, or until the chicken reaches an internal temperature of 165°F and the vegetables are tender and nicely charred.
While the chicken and vegetables roast, prepare the creamy tahini dressing by whisking together tahini, water, a pinch of salt, and a little extra lemon juice if desired to achieve a smooth consistency.
Remove the chicken and vegetables from the oven, slice the chicken if desired, and drizzle the tahini dressing over the top before serving.