I think this is a good way to stretch a buck. It makes a big casserole pan and leftovers can be frozen. I usually save those in freezer bags for when Im not home this way I know my husband has a healthy and home cooked meal.
In a small sauce pan poach your chicken, add water and put on the stove bring to a boil and then let it simmer for about 30 mins. (I got busy so mine was on for about an hour) Cool in broth. Skim the foam off the top.
In another pot add water for your spaghetti. While waiting for water to come to a boil break spaghetti into 1 inch pieces. Cook pasta according to package and drain when pasta is cooked add some butter. (I put the spaghetti into the baking dish Im going to use . This way I can sautee the veggies in the same pot I just cooked the spaghetti in and saves on clean up) You can salt your pasta water...
Add some olive oil to your pot and add onions sautee til golden add celery and then add mushrooms. Stir well. When the mushrooms are cooked thru (about 5 mins) add the garlic stir it in and sautee for a few mins.
Add 2 tablespoons of flour to your veggies stir it in until it all dissolves then add the sherry and chicken broth (use the broth that you poached the chicken in)bring to a boil until broth thickens.
When the broth thickens up add your pasta to the sauce and mix well. Put back into your baking dish top with some grated cheese and bake @ 350 until top gets lightly browned.