Preheat a cast iron grill pan on medium low flame.
Butter the outside of each slice of bread with a thin layer of butter.
Top the inside of each panino with half of the cheese, the arugula leaves, the chicken, broiled tomatoes, the remaining of the cheese and the bread. Press gently together for the filling to hold together a bit.
Grill the panini for about 3 minutes on each side, loosely covered with aluminum foil; until golden brown and the cheese has melted.
Notes
You can substitute fresh cherry tomatoes for the roasted tomatoes.