Bring a large pot of lightly salted water to a boil. Add pasta and cook for 8 to 10 minutes or until al dente; drain.
Preheat oven to 350 degrees F (175 degrees C).
In a skillet over medium heat, brown the ground beef. Drain and crumble. Put crumbled beef in skillet. Stir in salt, pepper, garlic powder, bell pepper and pasta sauce. Bring to a boil; reduce heat and simmer for 20 minutes.
In a small bowl combine sour cream, green onions and cream cheese and set aside. Coat a 9x13 inch baking dish with cooking spray and add the cooked spaghetti. Spread the cream cheese mixture over it, add the meat mixture and sprinkle with Cheddar Cheese.
Cover and bake for 25 minutes. Uncover and bake for 5 more minutes until the cheese is bubbly.