Start by making the artichoke spread; combine all of the artichoke spread ingredients in a bowl and set aside.
To prepare the chicken, combine all chicken ingredients, except the vegetable oil, and toss together. Preheat a panini grill pan over medium heat for 3 - 4 minutes. Brush the grill lightly with vegetable oil. Reduce the heat to medium and arrange the chicken breasts on the grill.
Cook the chicken breasts 5 - 6 minutes on each side or until cooked through and tender. Remove the chicken from the grill and cool slightly. Carefully slice each breast in half horizontally.
To assemble the paninis, divide the artichoke spread equally and spoon onto each cut side of bread. Layer one cut side of bread with a slice of chicken, a slice of cheese and the spinach/arugula leaves. Cover each with one of the remaining pieces of bread. Press the sandwiches firmly together.
Brush both sides of each sandwich with olive oil. Preheat the panini grill pan over medium heat for 3 - 4 minutes.
Place the sandwiches on the hot pan. Place the press on top of the sandwiches and cook for 2 - 3 minutes, or until golden and crispy. Carefully turn each sandwich, cover with the press and cook the other side for 1 - 2 minutes.
Transfer the sandwiches to a serving plate and serve hot.