Thaw escalloped chicken and noodles in refrigerator overnight.
Melt butter in a large skillet over medium-high heat. Add onion and bell pepper; sauté until tender. Add cheese, and cook, stirring constantly, until cheese melts. Stir in escalloped chicken and noodles, diced pimiento, and pepper. Spoon into a lightly greased 9-inch square baking dish. Sprinkle with breadcrumbs.
Bake at 350° for 25 minutes.