In a large mixing bowl, coat the chicken breasts with 1/2 cup of pesto, ensuring they are fully covered. Let them marinate while you prepare the veggies.
On a large sheet pan, arrange the cherry tomatoes, broccoli florets, sliced bell pepper, and red onion. Drizzle with olive oil and season with salt and pepper. Toss to coat the vegetables evenly.
Create spaces in the center of the veggies for the marinated chicken breasts and place them on the sheet pan.
Spoon the remaining pesto over the chicken breasts for extra flavor.
Bake in the preheated oven for 25-30 minutes, or until the chicken is cooked through and reaches an internal temperature of 165°F (75°C) and the vegetables are tender.
Once cooked, remove the sheet pan from the oven and let it rest for 5 minutes.