Preheat grill to medium. (Around 450 degrees if you have a thermometer to check.) Place 6 or 8 toothpicks in water to soak. (This will keep them from burning on the grill.)
While the grill heats, carefully slice a deep pocket in the loin filet lengthwise. You want to keep the knife flat (away from your hand!) and cut the length of the meat, leaving the ends and back side uncut.
Spread tomatoes evenly inside the pocket, and arrange cheese over the tomatoes so it fits mostly inside when the pork is pulled closed. Use the toothpicks to hold the sides of the pork together and contain the filling.
Place the stuffed pork onto the hot grill with the stuffed side up. Close the lid, and cook for 15 minutes.
Open the lid, tilt the pork loin onto one side, but don’t flip over completely. You do not want the filling directly on the grill. Some juices will drip out, which is OK. Close lid again, and cook five minutes. Open, and repeat on other side.
At this point, the pork should be fully cooked, but check the temperature deep inside and near the top of the pork to make sure it’s over 145 degrees F. Remove from heat, and allow to stand for a few minutes before slicing and serving.
All grills are different, so check your pork every few minutes. If your grill is hotter or cooler than mine, your cooking times may vary.
This recipe can also be prepared in the oven. Just bake it at 425 degrees for 30-40 minutes or until internal temperature reaches 145 degrees F and cheese is melted.