Heat the oven to 375°F. Cook pancetta in a wide saucepan over medium heat for 6 to 8 minutes until lightly crisp, then spoon off all but 1 tablespoon rendered fat.
Add shallot and cook for 2 minutes, then stir in garlic for 30 seconds. Add tomatoes, cream, water and pepper and simmer gently for 5 minutes.
Boil tortellini in water with the tablespoon salt for just 1 minute, then drain gently. Fold into the sauce with frozen peas.
Transfer to a deep 9-by-13-inch baking dish, scatter with mozzarella and Parmesan and cover with foil. Bake for 20 minutes.
Uncover for 8 to 10 minutes until the filling of a center tortellino and the surrounding sauce reach 165°F. Rest for 5 minutes before serving.