California Avocado-Rosemary Chicken and Pancetta Panini

Ingredients

 * 6 boneless and skinless chicken breast halves
 * olive oil, as needed
 * 2 tsp finely chopped fresh rosemary
 * 3 cloves garlic, chopped finely
 * 1 California avocado
 * 1 tbsp lemon juice
 * 1 tsp finely chopped lemon zest
 * salt, as needed
 * pepper, as needed
 * 3 tbsp mayonnaise
 * 12 pieces focaccia, about 4" x 5" each
 * 2 medium tomatoes, sliced
 * 6 slices (rounds) pancetta (Italian bacon), fried crisp. Two to three slices of bacon may be substituted for each slice of pancetta.
 * arugula leaves as needed

Directions

 * 1) Pound each chicken breast half to an even thickness, about ⅜".
 * 2) To pound chicken, put 1 breast half between two pieces of plastic wrap.
 * 3) Pound with mallet or the flat side of a french knife to desired thickness, repeat with remaining chicken.
 * 4) Lightly coat each piece with olive oil; rub each with some of the rosemary and garlic.
 * 5) Marinate in the refrigerator for at least 3 hours or up to 12.

To prepare sandwiches

 * 1) Roughly mash avocado; stir in lemon juice and zest; reserve.
 * 2) Season chicken with salt and pepper.
 * 3) In a frying pan lightly filmed with olive oil, pan-grill chicken until just firm to the touch, 2 to 3 minutes per side; reserve.
 * 4) Spread a generous tablespoon of the avocado mixture on 6 pieces of focaccia; spread ½ tablespoon mayonnaise on remaining pieces of focaccia, mayonnaise-side down.
 * 5) Lightly film a large, hot frying pan with olive oil.
 * 6) Pan grill sandwiches, lightly pressing down on each with a spatula, as they cook, until focaccia is browned on the bottom.
 * 7) Turn; repeat procedure.
 * 8) Cut each sandwich in half diagonally.