Seed and devein the peppers. You can just cut the tops off if you want to stuff a whole pepper or cut them in half lengthwise as I did. For a more tender pepper, bring a pot of salted water to boil and cook the peppers for 5 minutes, then drain. Lay the peppers on a foil lined baking sheet.
Preheat the oven to 350 F.
In a large skillet, brown the ground beef and onion until the meat is cooked through and the onion is soft. Drain any excess fat.
Add the salt and pepper, tomato sauce, rice and Worcestershire sauce. Stir together and bring to a simmer. Cover and cook for 20 minutes, stirring now and then.
If you want to add sliced peppers, stir them into the meat mix now. If you wan to add peppers only to some of the peppers, you can just add them as you stuff the pepper.
Lay half a slice of cheese on the bottom of a pepper, top with the ground beef and rice mix, then add the other half of the cheese slice to the top.
Bake uncovered for 30 minutes.