Preheat oven to 425°.
Combine first 3 ingredients in a bowl; stir with a fork until well blended. Shape dough into a ball; coat with cooking spray. Cover and let stand 5 minutes. Press dough in bottom and 1 inch up sides of a 10-inch cast-iron skillet coated with cooking spray; prick several times with a fork. Bake at 425° for 5 minutes.
Combine tomato sauce and Italian seasoning; spread over crust. Top with sausage, mushrooms, peppers, and cheese. Bake at 425° for 20 minutes or until cheese melts and crust is golden. Let stand 10 minutes before serving.