Preheating the Oven: Begin by setting the oven to a temperature of 350 degrees Fahrenheit to ensure it reaches the correct temperature for baking.
Sautéing Onions: In a skillet, melt the light butter over medium heat. Add the sliced onion and sauté until it becomes translucent and slightly golden. Once done, remove the onions from the skillet and set them aside.
Preparing the Chicken: Season the chicken breasts evenly with the paprika, garlic powder, and salt. Using the same skillet, increase the heat to medium-high and spray it lightly with cooking spray. Add the chicken breasts to the skillet and sear them on both sides until browned, approximately 5 minutes per side.
Combining the Ingredients: Return the sautéed onions to the skillet with the chicken. Open the can of French onion soup and pour it over the chicken and onions. Allow the mixture to cook for about 5 minutes or until the soup reduces slightly and thickens, ensuring that the chicken is thoroughly coated with the sauce.
Baking the Dish: If you are using a cast-iron skillet, you can proceed by sprinkling the mozzarella cheese evenly over the chicken. Place the skillet directly into the preheated oven. If not using a cast-iron skillet, transfer the chicken, onions, and sauce into a suitable baking dish, then top with the mozzarella cheese. Bake in the preheated oven for 15 to 20 minutes, or until the cheese has melted and the sauce is bubbling.