Preheat oven to 450 degrees. Spray baking sheet with nonstick cooking spray.
Wash the peppers. Slice them length wise in half and remove the seeds and white membranes. Set aside.
To a large bowl add ground beef, ketchup, Worcestershire sauce, onion and mix with cheese, until thoroughly combined. Fill peppers with approximately 1 heaping tablespoon of beef mixture. The bigger the pepper, the more filling you will use. Secure the pepper with a toothpick pierced through the middle if necessary for the jalapeño to hold its form. Season to taste with salt and pepper.
Place peppers on the prepared baking sheet and bake for 20 minutes. Remove from oven and sprinkle a bit more cheese over poppers. Return to oven until cheese melts. Transfer to serving platter and enjoy!
Make these bacon cheeseburger jalapeno poppers by throwing chopped cooked bacon into the cheeseburger mixture!