Heat the oven to 425°F and line a rimmed sheet pan with foil.
Coat the chicken with 1/4 cup pesto, salt and black pepper and arrange the cutlets in a single layer.
Roast for 14 minutes, turn the chicken and roast for 4 to 6 minutes more.
Top each cutlet with mozzarella and return the pan to the oven for 2 minutes, until the cheese melts and the chicken reaches 165°F.
Rest the chicken for 5 minutes and warm the focaccia in the switched-off oven for 2 minutes.
Stir the mayonnaise with the remaining pesto and assemble each focaccia square with pesto mayo, 1 cheesy chicken cutlet and 1/4 cup roasted pepper strips.