Use butter, not Olive oil. Omit garlic. Double cheese (half mozzarella, half parmesan). I cooked this at 350 for 30 minutes instead of what the recipe called for. It was perfect :-)
Instead of baking chicken for 20 min, sear each side on high heat in olive oil, making sure to keep the middle pink. This locked in the juices; it was so moist, I didn't even need a knife to cut the chicken. After layering spinach, sauce, chicken, and cheese, bake in oven at 350 for 20-25 min.