I've done it like benniesdad mentions above. Precook many of the ingredients before rolling them up in the loin. First I trim off the fat & silver skin. Then I start the fillet/slice about 1" from the top of the loin and slice to about 2/3 of the way in, then 1" down and then back to the front where I started stopping about 1" short, basically making a trifold. There are instructions on the interwebs on how to fillet a pork loin. I use butcher's string to lace it back up. Just be careful not to overload it. It's hard to roll back up & the guts start oozing out when it's cooking, especially cheese. I always go to 150F internal, wrap in HD Foil, wrap in a towel and into the cooler for at least 1/2 hour but prefer an hour. Never had a dry loin yet...
My favorite is Pizza Roll. Browned sausage, sautéed onions & peppers, pepperoni, mozzarella cheese, dried basil, and what ever else happens to be handy. Serve with a little pizza sauce over the slice of loin and dusted with parmesan cheese with garlic bread on the side. Cheers!!!
If Homebrew & BBQ aren't the answer, then you're askin' the wrong questions... Cheers!!!