Preheat oven to 375 degrees. Lightly spray a 9x13-inch pan with cooking spray.
Mix together Bisquick, parmesan cheese, garlic powder and milk. Drop half of dough by heaping tablespoons in bottom of prepared pan. It will not cover entire pan. Spread half of sauce over dumplings. Top with half of sausage, pepperoni and cheese.
Drop remaining dough in pan and top with remaining sauce, sausage, pepperoni. Top with remaining cheese. Sprinkle oregano over casserole.
Bake for 30 minutes, until dumplings are done and cheese is bubbly.