Start by prepping all your ingredients. Thaw and drain the spinach, slice or shred your mozzarella, and prepare your seasonings. At the same time, preheat the oven to 400 Fahrenheit (200 Celsius).
If you’re using fresh chicken breasts, cut them in half and pound them out to an even thickness. This will ensure they cook evenly and quickly.
Place the spinach and some mozzarella into the center of each chicken breast, then roll or fold them over to enclose the filling.
Place the stuffed chicken breasts into your casserole dish, add spinach in between the rolls of chicken and place the remaining mozzarella on top. Bake in the oven for 45 minutes at 400 Fahrenheit (200 Celsius) or until the chicken is cooked and the cheese is bubbly.
