01 - Preheat oven to 375 degrees Fahrenheit.
02 - Slice tops off bell peppers and remove seeds and inner membranes. Arrange upright in a baking dish.
03 - In a large skillet over medium heat, cook the Italian sausage, breaking it up with a spoon, until evenly browned and fully cooked, about 5 to 7 minutes. Drain excess fat if necessary.
04 - Add chopped onion and minced garlic to the skillet. Sauté until the onion softens, about 3 minutes.
05 - Stir in cooked rice, Alfredo sauce, grated Parmesan, 1/2 cup of the shredded mozzarella, parsley, dried Italian herbs, black pepper, and salt. Mix until thoroughly combined and warmed through.
06 - Evenly fill each prepared bell pepper with the sausage mixture, gently pressing down to compact.
07 - Sprinkle the remaining 1/2 cup shredded mozzarella over the tops of the stuffed peppers.
08 - Pour water or chicken broth into the bottom of the baking dish. Cover the dish loosely with aluminum foil.
09 - Bake for 30 minutes. Remove foil and continue baking for 10 additional minutes, until peppers are tender and the cheese is golden and bubbling.
10 - Allow stuffed peppers to cool slightly. Garnish with extra parsley if desired and serve hot.