In a small bowl, add all of the Marinade ingredients and whisk together until well combined. Use a fork to pierce each chicken breast in several places and then place the chicken breasts in a medium-sized glass baking dish. Pour Marinade over the chicken breasts; cover and refrigerate overnight.

Place a large frying pan over medium-high heat. Once hot, add 2 Tbsp of olive oil and sliced peppers. Saute for 5-6 minutes, and then add the sliced onions. Continue sautéing over medium heat, stirring occasionally, for 15-18 more minutes or until peppers and onions are soft.

Meanwhile, place another large frying pan or grill pan over medium-high heat. Remove chicken breasts from marinade and place in the pan. Discard marinade. Cook chicken until done (~15-18 minutes), flipping after 10 minutes.

Once chicken is done, transfer to a cutting board and slice into ¾” strips.

Place a grill pan or frying pan over medium heat and brush with the remaining 2 tsp of olive oil. Place the bottom half of each ciabatta roll in the pan. Top each sandwich with ¼ cup of Monterey Jack cheese, 1/3 cup of sautéed onions and peppers, and several strips of grilled chicken. Sprinkle a little more Monterey Jack cheese on top and then place the remaining half of the ciabatta roll on top. Cook over medium heat for 4-5 minutes per side, or until cheese is fully melted.

Serve hot with a side of salsa for dipping (optional).