If you have never made stuffed meat before, I heartily recommend watching this youtube tutorial for how to slice open the meat. It was very helpful for me.
I started with this recipe as a basis, but altered it a lot.
I think this same filling combination would be awesome in a turkey breast, although you'll have to do your own research on how to slice the sucker. ☺
1 pork loin (I don't know how many pounds, but mine was about 12inches long..3ish pounds maybe?)
1 c sour cream
1/2-3/4 c shredded mozzarella cheese
1/2-3/4 (10 oz) package of frozen spinach, thawed (about 1 1/2 c cooked and chopped), and well drained
1/2 c diced onion
2-3 cloves minced garlic (I did 5...)
1/3 c dry bread crumbs
a few Tbs olive oil
1 tsp salt
1 tsp pepper
string (I made due with thread, but that tends to cut into the meat, so string is much better)
Cut open roast according to directions in tutorial, so that is lays flat.
Spread sour cream evenly over meat.
Sprinkle mozzarella evenly over sour cream.
Saute onions in a little olive oil until they get soft and glassy--but not browned (optional), then mix spinach, garlic, onion, bread crumbs, salt, and pepper together in a bowl. Put in the olive oil from the onions, plus a little extra as needed to make the mixture stick together (it should not be crumbly nor slimy, but just kinda gooshy...) Sprinkled spinach mixture evenly over the mozzarella on the meat.
Roll up the meat log, and tie closed to secure it. Then carefully transfer it to a pan.
Bake, uncovered, at 325 for about 1 to 1 1/2 hours. It is done when the internal temperature reaches 160* (use a food thermometer, if you overcook it it will be very dry, but if you undercook it it won't be safe). I hear that you can cook it to about 135 or 140, then take it out and 'tent it' (cover it with foil while still in the hot pan) and let it sit for about 15 minutes, then it will finish cooking in its tent. I have not done this personally, so I don't know. ☺