In a small bowl, combine marinara sauce and basil, blending well; set aside.
With a sharp knife, remove stems from mushrooms; coarsely chop stems and set aside.
Arrange mushrooms, rounded-side-down in a 12 x 8 x 2-inch baking dish and set aside. In a medium bowl, combine chicken, marinara/basil sauce, garlic, green onion, peppers, Italian parsley, and Italian herbs, if desired, mixing well. May add salt and pepper to taste, if desired.
Press mixture onto mushrooms, dividing evenly and fitting each mushroom.
Bake, loosely covered with aluminum foil, in a preheated moderate oven (350 degrees F.) for 20 to 25 minutes.
Uncover and sprinkle each mushroom with shredded mozzarella cheese or cheese of choice and continue baking, uncovered, for 6 to 7 minutes, or until cheese is melted.
Sprinkle each lightly with Parmesan or Romano cheese, if desired, and continue baking for 6 to 8 minutes or until cheese becomes lightly browned.