Heat oven to 400°F. Spray 8-inch square (2-quart) baking dish with cooking spray. Spread spaghetti evenly in dish; set aside.
In 12-inch nonstick skillet heat 1 tablespoon of the butter over medium-high heat. Add onions, cook, stirring occasionally, 1 to 2 minutes or until translucent. Stir in chicken broth, cream, cream cheese, salt, pepper, stirring occasionally, cook 4 to 5 minutes or until cheese is melted. Stir in chicken.
Pour chicken mixture over pasta in dish; stir (baking dish will be full). Cover tightly with foil. Bake 25 to 30 minutes, stirring well halfway through bake time until spaghetti is tender.
Meanwhile, in small bowl, melt remaining 1 tablespoon of the butter. Stir in breadcrumbs and Parmesan cheese until well blended.
Remove foil from baking dish. Stir peas into spaghetti mixture. Sprinkle spaghetti mixture evenly with breadcrumb mixture. Bake uncovered 8 to 10 minutes longer or until crumbs are golden brown. Serve immediately.
You can find pre-shredded rotisserie chicken in the deli section of your favorite grocery store. Complete this meal with a mixed green salad.