Cut each piece of focaccia bread in half and set aside.
Preheat an indoor grill over medium-high heat. Horizontally slice the chicken breasts in half. Grill chicken on each side for about 4-5 minutes, until cooked through and the juices run clear. Remove from heat and set aside.
Assemble the focaccia sandwiches by topping a piece of bread with ½ tbsp pesto, grilled chicken cutlet, mozzarella, tomato slices, 3 basil leaves, ½ tbsp pesto, and the other piece of focaccia. Repeat with remaining ingredients.
Place the sandwiches onto a panini press or indoor grill set to medium heat. Cook until the bread is golden and the cheese has melted. Serve immediately.