Finely chop onion. Set aside.In a large dutch oven brown hamburger and onion until hamburger is no longer pink and the onion is translucent. Drain off access fat. Return to pot. Add Spaghetti sauce and the chili-o-seasoning. Stir.
In another large pot boil the shells till al dente. Drain.
Combine meat mixture with shells and stir carefully as to not tear the shells.