Toss the pesto in with the chicken, making sure everything is coated.
Prepare the panini. Layer the chicken, sun-dried tomatoes and mozzarella slices between the bread.
Preheat a ridged fry pan or grill pan over medium heat until hot. Spray with cooking spray. Place the panini in the pan and weight down with a second fry pan or a grill press. Cook until the underside is golden, about 2 ½ minutes. Turn the sandwich over, weigh it down again and cook until golden on the other side, about 2 ½ minutes. Alternatively, you can cook the sandwiches using an electric panini press according to the manufacturer’s instructions.
Cut in half and serve immediately.
Notes
To save time, break out this sandwich when you have leftover chicken or a rotisserie chicken.
If you don't like sun-dried tomatoes, try roasted red peppers.
Don't leave the panini on the pan/grill long or you will burn it. Check every minute or so until you get the nice char marks.