This stuffed bread loaf, loosely based on the vegetable and meat mixtures found in Italy, is tasty either hot or at room temperature. Using a tube of refrigerated pizza dough saves time.
Preheat oven to 400° F. Spray a large baking sheet with non-stick cooking spray.
Heat 1-½ tablespoons of the oil in a large frying pan. Add garlic and onions and cook, stirring frequently, for 2 minutes. Stir in spinach, celery, ham (if using), and bell peppers. Continue cooking for 5 minutes, stirring frequently, or until spinach is wilted. Add mushrooms and olives, and cook 2 minutes longer, stirring constantly.
Scrape the mixture into a colander set over a bowl to cool.
Roll out the dough to a 10x12-inch rectangle. (The dough should be about ½ inch thick.) Oil the surface with the remaining ½ tablespoon olive oil.
Cover the dough to within an inch of the edges with the filling. Sprinkle with mozzarella and Parmesan.
With the longest edge parallel to you, roll up the dough like a jelly roll, tuck the ends under, and place it diagonally, seam side down, on a prepared baking sheet. Cut two deep slashes in the top to allow steam to escape.
Immediately bake for 40 to 50 minutes, or until bread is cooked through and top is golden brown. Cool thoroughly before cutting into slices.