Preheat oven to 375 degrees F.
Cut carefully cut tops off of the peppers and discard, along with any seeds. Set prepped peppers into a baking dish.
In a large skillet over medium heat, add oil. Once hot, add ground beef. Brown meat, breaking it up as you go, until partially cooked through.
Once the meat is mostly cooked, add diced onion. Cook an additional 5 minutes, until meat is cooked through and the onions have softened.
Add worcestershire sauce, spices, ketchup, and mustard, Stir to combine.
Add cooked rice and cheese (reserving ½ cup of cheese for topping). Stir to combine.
Stuff peppers to the top of each, until all the filling is used up. Top each pepper with the remaining cheese and place in the oven. Bake for 30 minutes, or until the peppers have softened and the cheese is melted.
Serve as is or with your favorite burger toppings.