Cook pasta to package directions. Meanwhile, in a large skillet over medium heat, cook the chicken, onion, salt and pepperin oil until chicken is no longer pink. Stir in Alfredo sauce; bring to a boil. Stir in cheeses, salsa, and taco seasoning.
Drain pasta; toss with chicken mixture. Divide between two greased 8-in. square baking dishes.
Cover and freeze one casserole for up to 3 months. Cover and bake the remaining casserole at 350 degrees for 30-35 minutes or until bubbly.
To use frozen casserole: Thaw casserole in the fridge overnight. Remove from fridge 30 minutes before baking. Cover and bake at 350 degrees for 50-60 minutes or until bubbly.