Preheat the Oven: Begin by preheating the oven to 400 degrees Fahrenheit.
Sauté Onions: In a large, oven-safe skillet, heat the olive oil over medium-high heat. Add the chopped onion and sauté for approximately 2-3 minutes, or until the onions have softened and the edges begin to take on a slight golden color.
Add Garlic and Tomatoes: Introduce the minced garlic to the skillet and sauté for about 30 seconds, just until it becomes fragrant. Following this, add the crushed tomatoes along with the Italian seasoning, garlic powder, crushed red pepper, salt, and pepper. Continue to sauté for an additional 2 minutes to allow the flavors to meld.
Brown the Chicken: Place the chicken breasts in the skillet, cooking them for 1-2 minutes on each side to slightly brown them.
Bake the Chicken: Transfer the skillet to the preheated oven and bake the chicken for 10 minutes. After the initial baking period, flip the chicken breasts over.
Add Mozzarella and Finish Baking: Top each chicken breast with slices of fresh mozzarella cheese (or shredded mozzarella, if using) and return the skillet to the oven. Bake for another 10 minutes, or until the chicken is thoroughly cooked to an internal temperature of 165 degrees Fahrenheit.
Garnish and Serve: Remove the skillet from the oven, garnish the chicken with fresh basil, and serve immediately.