Step 1: Season the Chicken

1. Prepare the Chicken: Pat the chicken breasts dry with paper towels to remove excess moisture. This helps create a better sear when cooking.
2. Season: In a small bowl, mix the salt, black pepper, and paprika. Sprinkle this mixture evenly over both sides of the chicken breasts, ensuring they’re well-coated.

Step 2: Sear the Chicken

1. Heat the Oil: In a large skillet or cast-iron pan, heat 2 tablespoons of olive oil over medium-high heat. Make sure the pan is hot before adding the chicken, as this will help develop a golden crust.
2. Sear the Chicken: Place the chicken breasts in the skillet and cook for about 4-5 minutes on each side, or until they’re golden brown. They don’t need to be fully cooked at this stage, as they will finish cooking in the sauce. Once browned, transfer the chicken to a plate and set aside.

Step 3: Make the Garlic Tomato Sauce

1. Sauté the Onion: In the same skillet, add the chopped onion and cook for 3-4 minutes, or until it becomes translucent and soft, stirring occasionally. If the pan seems dry, add a bit more olive oil.
2. Add the Garlic: Add the minced garlic to the skillet and cook for 1 minute, stirring constantly. Be careful not to let the garlic burn, as it can become bitter.
3. Add the Tomatoes: Add the diced tomatoes (or halved cherry tomatoes) to the skillet, along with the balsamic vinegar, Italian seasoning, and red pepper flakes if using. Stir to combine and let the mixture simmer for 5-7 minutes, allowing the flavors to meld together and the sauce to thicken slightly.
4. Optional Add-Ins: If you’re adding spinach or mushrooms, stir them into the sauce at this stage and cook until softened.

Step 4: Simmer the Chicken in the Sauce

1. Return the Chicken to the Skillet: Place the seared chicken breasts back into the skillet, nestling them into the tomato sauce. Spoon some of the sauce over the chicken to ensure it’s well-coated.
2. Simmer: Reduce the heat to low, cover the skillet, and let the chicken simmer in the sauce for about 10 minutes, or until it’s cooked through and reaches an internal temperature of 165°F (74°C).

Step 5: Add the Mozzarella

1. Add the Mozzarella: Sprinkle the shredded mozzarella over each chicken breast (or place a slice of fresh mozzarella on each one). Cover the skillet again and cook for an additional 2-3 minutes, or until the cheese is melted and bubbly.
2. Broiling Option: For an extra-golden, bubbly cheese topping, transfer the skillet to a preheated broiler for 1-2 minutes, watching carefully to prevent burning.

Step 6: Garnish and Serve

1. Garnish: Remove the skillet from the heat and sprinkle fresh basil leaves over the top for a burst of color and flavor.
2. Serve: Serve the Garlic Tomato Chicken with your choice of pasta, rice, or crusty bread, spooning some of the tomato sauce over each serving. This dish is also delicious with a side salad or roasted vegetables.