On a 12- by 15-inch baking sheet, unroll pizza crust dough.
Squeeze excess moisture from spinach. Mix spinach, ricotta cheese, parmesan cheese, nutmeg, and garlic.
Spread mixture evenly over dough.
Starting at a long edge of dough, roll to enclose filling. Set the loaf, seam down, on baking sheet. Brush loaf top with olive oil.
Bake in a 425° oven until well browned, 12 to 15 minutes. Meanwhile, stir marinara sauce in a 1- to 1 1/2-quart pan over medium heat until hot; or heat in a microwave-safe bowl in a microwave oven at full power (100%) until hot.
Slice loaf diagonally, making 10 equal portions. Offer 1 slice as an appetizer serving, or 2 slices as a main-dish sandwich. Spoon marinara sauce over slices to taste.
I tried a variation of this recipe that omitted the spinach and used a mix of ricotta and feta, with garlic, sliced kalamata olives and sun-dried tomatoes. It looked lovely before going into the oven but the filling burst out one side during baking. I don't know if there was simply too much filling (I had twice as much dough and thus doubled the filling) or if the spinach would have had a "stabilizing" effect. It still tasted good but of course looked funny, and I sheepishly served it at a get-together. I might still try the actual recipe, but not knowing if this would happen again we would at least eat it at home, and may add an egg to the filling.