Heat oil in large nonstick skillet on medium heat. Add onions and saute 5 minutes or until tender. Stir in taco seasoning and tomatoes. Stir to combine and cook a few more minutes. Add chicken, beans and half each of the green onions and cilantro. Stir and let warm through. Remove from heat.
Add cooked pasta to chicken mixture. Stir and pour into greased 13x9" baking dish. To with grated cheese.
Bake 20 to 25 minutes or until pasta mixture is heated through and cheese is melted.
We serve it family style with some bowls of fixins allowing everyone to add what they like.