For the dough: Whisk together the warm water, yeast and sugar in a bowl. Set aside until the yeast activates and becomes foamy, about 10 minutes.
Whisk the flour and salt in a large bowl. Make a well in the center. Pour the foamy yeast mixture and the olive oil into the well. Using a fork, gradually incorporate the flour into the liquid mixture. Turn the dough onto a lightly floured surface and knead until very smooth, about 5 minutes.
Put the dough in a lightly oiled bowl and cover with plastic wrap. Place in a warm area until the dough doubles in size, about 2 hours.
For the topping: In the meantime, mostly drain the clams, retaining about 2 tablespoons liquid. Mix together the chopped clams and juice, olive oil, oregano and garlic in a bowl. Keep refrigerated until ready to use.
Preheat the oven to 500 degrees F and adjust the rack to the lowest level. Put a pizza stone or turned-over baking sheet on the rack.
When the dough has doubled in size, turn onto a lightly floured surface and stretch into a very thin rectangle, about 12 by 14 inches. Dust a pizza paddle or turned-over baking sheet with the cornmeal and place the dough on top; make sure it slides back and forth easily. If using, sprinkle the mozzarella all over the dough. Top evenly with the clam mixture and the Parmesan. Season with salt.
Carefully slide the dough onto the hot pizza stone. Cook until nicely golden brown on top and bottom, 8 to 10 minutes. Sprinkle with the parsley and crushed red pepper. Drizzle with more olive oil if desired.