Heat oil in 12-inch nonstick skillet over medium-high heat and cook green pepper, stirring occasionally, 3 minutes. Add ground beef and cook, stirring occasionally; drain.
Stir in sauce and chili powder. Bring to a boil over high heat. Reduce heat to low and simmer covered 10 minutes.
Stir in macaroni and heat through. Serve, if desired, with sour cream and shredded Cheddar cheese.