Cook beef and bell pepper in a large skillet over medium-high heat, stirring until beef crumbles and is no longer pink; drain. Stir in water, tomato paste, and sauce mix. Cover, reduce heat to low, and simmer 10 minutes.
Sprinkle half of Parmesan cheese on bottom of frozen pastry shell; top with half of meat mixture, and sprinkle with 1 cup mozzarella cheese. Top with remaining meat mixture and Parmesan cheese. Place shell on a baking sheet.
Bake on lowest oven rack at 400° for 20 minutes. Sprinkle with remaining mozzarella cheese; bake 5 more minutes or until cheese melts.