Preheat the oven to 375° Spray a baking dish with non-stick cooking spray or brush with olive oil.  Rinse and pat dry chicken breasts. Place chicken in the baking dish, season with kosher salt and pepper, and coat with pesto (about 2 tbsp per chicken breast, depending on the size).

Bake chicken in the oven for 20-30 minutes, until cooked through and internal temperature reaches 165° Remove from the oven and set aside.

Prepare a baking sheet with parchment paper. Place ciabatta rolls cut side up on the baking sheet and brush with olive oil.  Place in the oven and cook until slightly browned.

In the meantime, cut chicken into 1-2” pieces. When the bread comes out of the oven, layer with mozzarella, the roasted red peppers, chicken, and red onion.  Return to the oven and bake until the cheese has melted and all of the toppings are hot.