Preheat oven to 400 degrees.Cook spaghetti according to package directions. Drain and place in the bottom of a greased 9x13 casserole dish. At the same time, brown hamburger meat. Add onions and peppers to meat and cook until softened. Add sauce to meat mixture and simmer on low heat until heated through. Mix together cream cheese, sour cream, garlic salt and parmesan cheese. Spread cream cheese mixture over noodles. Pour meat sauce over cream chesse layer. Top with the shredded cheese. Bake in 400 degree oven until top is lightly browned and bubbly.