Grilled Chicken Cheesy Panini

1 to 1-1/2 lbs. boneless, skinless chicken breast halves, pounded to about 1/2-inch thick
5 Tbsp. olive oil, divided
Coarse salt and ground pepper to taste
10 slices Sargento® Deli Style Sliced Vermont Sharp White Cheddar Cheese, divided
1 (15-inch) loaf crusty ciabatta bread
1 pkg. (12 oz.) guacamole
1 medium Roma tomato, thinly sliced
5 Tbsp. chopped fresh cilantro (optional)

Coat grate with cooking spray. Preheat grill to medium heat.
Lightly brush chicken with 3 Tbsp. olive oil; season with salt and pepper. Place on preheated grill and cook 3-5 minutes. Turn; place half of cheese on top and cook for 3-4 minutes more until cheese is melted. Remove from grill and cover with foil to keep warm.
Cut bread open, leaving end connected so top and bottom are hinged. Brush remaining oil on top and bottom of bread.
Place remaining cheese on bottom of bread, followed by guacamole, tomato and cilantro, if desired. Place chicken, cheese-side up, on top. Close sandwich with top of ciabatta and press down with spatula while grilling 1 to 2 minutes more. Remove from grill; cut in 5 pieces and serve.