In a large skillet, cook the sausage, onion and garlic over medium heat until meat is no longer pink; drain. Remove from the heat; stir in spinach and mushrooms. Add mozzarella cheese, salt, pepper and Parmesan cheese if desired; mix well and set aside.
Separate crescent dough into eight rectangles; seal perforations and flatten slightly to 5-in. x 4-1/2-in. rectangles. Place about 1/3 cup sausage mixture on half of each rectangle to within 1/2 in. of edges. Beat egg and water; brush on edges of dough. Bring unfilled half of dough over filling; press edges with a fork to seal. Brush tops with egg mixture. Sprinkle the cornmeal on a greased baking sheet; place pockets on baking sheet.
Bake at 350° for 15-20 minutes or until golden brown.
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