Preheat oven to 400 degrees F.
Brown ground beef, onion and pepper together in a large saute pan or deep skillet.
Add the tomatoes and Velveeta. Cook over low heat until cheese is melted.
Stir in cooked elbows.
Transfer to a 11 x 7 - inch baking dish. Top with shredded cheese and bake for 15-20 minutes, or until cheese is melted and bubbling.
Garnish with green onion if desired.
NOTE: If you cannot get Velveeta (outside US/Canada) then substitute 1/2 cup cream and 1/2 cup shredded cheddar)