First of all, let me make one thing perfectly clear, as one of our former presidents liked to say. Peperoni and pepperoni are not the same thing. They are false friends. Peperoni are bell peppers (pepperoni is salamino piccante, literally, "spicy little salami," which is what it is, after all). If you order a pepperoni pizza in Italy, you will get a pizza with bell peppers. You should ask for a pizza al salamino piccante or perhaps alla diavola.
Second of all. Italians usually make these in a different way from Americans, especially in rosticcerie (a sort of Italian fast food, which I will explain to you later, when I am in the mood). First of all, they will cut them horizontally and not vertically (see photo). I personally think this makes them easier to eat. Thirdly of all, they will really cook the peppers. Italians, unlike the Chinese, do not believe in semi-cooked peppers. They go the whole hog, right into limpsville. Fourthly of all, Italians show a distinct preference for red and/or yellow bell peppers (see photo again). I have never seen a stuffed green pepper in Italy. Not that there's anything wrong with that.
And finally. You need not stuff your peppers with meat, much less beef. You know what I've done more than once (although I'm not a vegetarian)? I've taken thawed or semi-thawed Gardenburgers, crumbled them, dressed them up as needed-some Parm, some olive oil, some tomato sauce, stuffed them in the ole horizontal red or yellow pepper and baked 'em! Mighty fine eatin'!