Preheat oven to 375 degrees
Dice the onion and saute in the olive oil
While the onion is cooking, remove the tops from the bell peppers and pull out all the seeds and white membrane
Mix all remaining ingredients in a bowl
Add onions to meat mixture and stuff the peppers
Cook peppers covered for 30 minutes
Remove the cover off the peppers, add a tablespoon of ketchup to each pepper and continue cooking for another 30 minutes
The peppers should be soft and the meat cooked through at this point (no longer pink)