Generously grease a 10x2-inch heavy round cake pan or 10-inch springform pan with oil. Sprinkle bottom of pan with cornmeal; set pan aside.
In a large bowl combine warm water and yeast, stirring to dissolve yeast. Let stand for 5 minutes. Stir in 1-1/2 cups of the flour, the 1/3 cup oil, and the salt. Beat with an electric mixer on low speed for 30 seconds, scraping side of bowl constantly. Beat on high speed for 2 minutes. Using a wooden spoon, stir in as much of the remaining flour as you can.
Turn dough out onto a lightly floured surface. Knead in enough of the remaining flour to make a moderately stiff dough that is smooth and elastic (6 to 8 minutes total). Shape dough into a ball. Place in a lightly greased bowl, turning once to grease surface. Cover and let rise in a warm place until double in size (50 to 60 minutes). Punch dough down. Cover and let rest for 5 minutes.
Place dough in the prepared pan. Using oiled hands, press and spread dough evenly over the bottom and 1-1/2 inches up the side of pan. Cover and let rise in a warm place until nearly double in size (30 to 35 minutes).
Preheat oven to 375 degrees F. For filling, in a medium skillet cook sausage over medium-high heat until brown. Drain in a colander. Using paper towels, pat sausage and wipe out skillet to remove additional fat. Return sausage to skillet. Stir in drained tomatoes, oregano, and snipped or dried basil. Cook and stir until heated through.
To assemble, arrange mozzarella cheese slices over dough. Spoon filling over cheese; sprinkle with 1/4 cup Parmesan cheese.
Bake for 45 to 55 minutes or until edge of crust is crisp and golden brown and filling is heated through. If necessary, cover crust with foil during the last 10 minutes of baking to prevent overbrowning. Cool on a wire rack for 10 minutes. If using a springform pan, remove side of pan. If desired, sprinkle with additional Parmesan cheese and basil leaves. Cut into wedges.