Chicken Tetrazzini

4 Tbls chopped onion
1 Tbls Butter
1 can Cream of Mushroom soup
1/2 cups water
1/2 cups cheddar cheese
1 cup cooked chicken
1 Tbls Parsley
1 Tbls chopped pimento (optional)
1/2 pounds cooked thin spaghetti

Saute onions in butter. Blend in soup, water and cheese. Stir until cheese is melted. Add chicken and rest of ingredients. Bake at 350F for 20-30 minutes or until heated through. I like to add a little bit of sour cream and add more cheese to top right before it goes in the oven.