Bring large pot of water to a boil. Add salt to the water. Cook the pasta for several minutes LESS than suggested. While the pasta cooks melt the butter in a skillet. Saute the mushrooms. Then add the onions, peppers and celery and cook to soften. Next stir in flour. Cook and stir for a minute. Break up the bouillon cube and add to the mixture in the skillet. Add the milk and stir to combine all ingredients. Remove the skin and bones from the canned salmon and add salmon AND the can juices to the skillet. Stir carefully as to not break up the salmon too much. Stir in the partially cooked drained spaghetti. Add Parmeesan cheese and stir. Pour the mixture into a greased casserole dish. Top with more Parmesan cheese if desired. Bake at 350 degrees for about 20-30 minutes or until bubbly. Remove from oven and allow to sit for about 15 minutes to firm up. Sprinkle with fresh parsley or other herbs if desired. Serve with a green salad and dinner is served!