Heat your grill to medium-high and brush with olive oil to prevent the chicken from sticking.
Place chicken in a zip close bag and use your heavy Calphalon skillet to pound the chicken to an even thickness. Pour the 1/2 cup of BBQ sauce in the bag to coat the chicken. Grill for 5-6 minutes on each side.
While the chicken is cooking set the oven to broil, and heat up a skillet to medium-high heat. Place the onions in the skillet once it is hot and cook, stirring occasionally, until the onions are caramelized (browned and softened). Remove the onions from the skillet and add the bacon to the hot skillet.
Turn the other skillet on to medium-high heat to warm it up. Place the grilled chicken into the hot, clean pan and put the remaining BBQ sauce on the chicken. Top with the caramelized onions, crispy bacon strips, diced tomatoes and then cover with cheese. Place the skillet into the oven under the broiler for 3-4 minutes or until the cheese is melted and bubbly.
Carefully remove the skillet from the oven and enjoy!