Preheat the oven to 350 degrees Fahrenheit.
In an oven safe skillet, melt butter on medium high heat and then add sliced onions and Worcestershire sauce. Sauté the onions in butter until softened and translucent. About 5-7 minutes.
When onions become soft, place onions on a plate and set aside.
Season each chicken breast with paprika, garlic powder, and kosher salt. Place seasoned chicken breasts into the prepared skillet.
Cook for 5 minutes on medium high, on both sides or until chicken breasts are golden brown.
While the chicken is cooking, whisk together the flour, french onion soup, and chicken broth in a small mixing bowl.
Add onions back into the skillet with the chicken breasts.
Pour in the French onion soup mixture. Simmer the chicken and onions for 2-3 minutes-this will allow the soup to caramelize the chicken.
Top each chicken breast with mozzarella cheese.
Place the skillet in a preheated oven.
Cook for 10-15 minutes or until bubbly.
Take out of the oven and let sit for 5 minutes before serving.