Preheat oven to 350 degrees. Salt the diced eggplant, and leave it in a colander for 20 minutes to rid of excess water.
Add the onion, spinach, mushrooms, olives, garlic, dried oregano, pepper flakes, canned crushed and diced tomatoes, and tomato paste into a Dutch Oven.
Squeeze water out of eggplant pieces and add to the Dutch Oven
Bring to a boil. Once boing, low to a medium simmer and cook, uncovered, for about 40 minutes until mushrooms and eggplant are soft.
Add in fresh basil, salt, and pepper, and stir.
Ladle into oven-proof bowls and sprinkle on top with mozzarella cheese. Bake for 10 minutes until cheese is bubbling and golden.
**Can add meatballs, uncured pepperoni, and/or chicken sausage to make a meat version