In a large skillet over medium heat add olive oil and butter. Add thinly sliced onions, a pinch of salt and pepper, and cook for about 12-15 minutes until the onions become very soft and a little caramelized.
Add 3 large chicken breasts to a slow cooker, followed by the cooked onions, minced garlic, chicken broth, and kosher salt & black pepper.
In a small bowl whisk together flour and Worcestershire sauce. Whisk the mixture into the broth on top of the chicken. Cook on low for 7-8 hours.
Remove the chicken, place onto a cutting board, and cut into pieces or lightly shred.
To assemble the sandwiches: Preheat oven to 415 degrees. On a sheet pan lay bottom of the roll down, top each roll with about 4 ounces of chicken, 1/4 cup of the au jus from the slow cooker, two tbsp of mozzarella, and then the top of the bun.
(Note: These totally work as open faced sandwiches for those who want to cut back on carbs or calories)
Place sheet pan into oven and bake for about 10 minutes or until the bread is crispy and the cheese is nicely melted. Serve with 1/2 cup of au jus for dipping! Enjoy!
*Points and Nutrition do not include hard roll because bread can vary due to size and brand.