In a large pot over high heat, boil water and boil jumbo pasta shells about 11-12 minutes instead of the recommended 14-16 minutes.
Cook pasta shells only until al dente.
The pasta will finish cooking when the dish is baked.
Drain the pasta shells and set aside. (I usually place the shells on waxed paper).
In a large skillet, pour olive oil.
Sauté mushrooms and green onions about 5 minutes.
Add garlic and sauté an additional couple of minutes.
In a large bowl, combine chicken, cream cheese, pesto sauce, Parmesan and Asiago cheeses (except for reserved topping ingredients), sautéed vegetables, salt, pepper and remaining seasonings.
Fill the pasta shells with the filling and place in a 9x13” baking dish that has been sprayed with cooking spray.
Cover with foil to prevent shells from drying out and hardening while baking.
Bake at 350° until shells are bubbling hot—about 30-40 minutes.
Sprinkle the remaining cheeses over filled shells and bake an additional 5-10 minutes until cheese melts.
Makes almost 3 dozen stuffed shells.
Garnish with fresh, minced parsley.