Preheat oven to 350. Bake chicken in lightly greased baking dish 25-30 minutes or until done; cool slightly and shred
Meanwhile, cook pasta according to package directions
*Optional* Saute mushrooms in hot oil in nonstick skillet over medium-high heat 5 minutes.
Combine chicken, pasta, mushrooms and peas in a bowl
Melt butter in a saucepan over medium heat; stir in flour. cook, stirring for 2 minutes or until bubbly; add milk; cook stirring constantly for 5 minutes or until thickened.
Stir in 2 tbsp cheese, salt and pepper. Add to pasta mixture.
Spoon into greased 11x7 baking dish; top with 2 tbsp cheese