Preheat your oven to 350 degrees Fahrenheit.
In an oven-safe skillet, melt butter over medium-high heat. Once melted, add the sliced onion and Worcestershire sauce. Sauté the onions, stirring occasionally, until they are softened and translucent, about 5 to 7 minutes.
When the onions are soft, transfer them to a plate and set aside.
Season each chicken breast with paprika, garlic powder, and kosher salt. This step is crucial for flavor.
Place the seasoned chicken breasts into the prepared skillet. Cook for about 5 minutes on medium-high heat on each side or until the chicken is golden brown.
While the chicken is cooking, whisk together flour, French onion soup, and chicken broth in a small mixing bowl.
Add the sautéed onions back into the skillet with the cooked chicken breasts.
Pour the French onion soup mixture over the chicken and onions. Allow it to simmer for about 2 to 3 minutes.
Top each chicken breast generously with mozzarella cheese.
Carefully place the skillet in the preheated oven. Bake for about 10 to 15 minutes or until the cheese is bubbly and golden.
Once done, take the skillet out of the oven and let it sit for about 5 minutes before serving.
