I really like sandwiches. But I loooooooooooooooooooooove porchetta sandwiches. I literally hunted down porchetta sandwiches when we were in Italy. One of the best eats near the Colosseum is Pane & Vino (Via Ostilia, 10, 00184).
It's a teeny tiny shop with a very friendly, English-speaking owner. His porchetta is delivered fresh every morning. Get the special porchetta with everything and just... eat in silence. And, if you're like me, grin like a fool.