1. Make Balsamic Reduction-Add balsamic vinegar into a small saucepan. Heat on low until vinegar begins to simmer. Stir occasionally until liquid is reduced by half. Be careful not to burn. Set pan with reduction aside to cool.
2. Prepare Chicken Filling-Heat sauté pan to medium-high heat. Add olive oil and then diced onions and cook until soft, about 2 minutes. Add garlic and cook until fragrant about 30 seconds more.
3. Add chicken to pan with the onions and garlic and season with Italian seasoning and salt and pepper to taste. Stir with spatula to combine all ingredients and cook in sauté pan until chicken is no longer pink, about 7 to 8 minutes. Once fully cooked reduce heat and add mascarpone cheese to mixture and stir until fully coated. Add diced sundried tomatoes, mix thoroughly and cook for 1 more minute. Remove sauté pan from heat.
4. Assemble Sandwich-With a long, serrated knife slice the focaccia bread horizontally through the middle to make a top half and bottom half. Set the top half aside. Distribute the arugula evenly on the bottom portion of the focaccia. Layer all of the cooked chicken mixture evenly on top of the arugula followed by a layer of the fresh mozzarella slices. Using a spoon, drizzle the balsamic reduction over the mozzarella and chicken. Lastly layer and evenly distribute the tomato slices on top of the mozzarella and cover with the top half of the focaccia.
5. Cut into 4 equal portions and enjoy!

Serves 4

Cook Chicken to and Internal Temperature of 165°F.