Scrub and wash the potatoes. Use a fork to poke a couple of holes in the top of the potatoes. Microwave the potatoes until they are soft and baked through. Ours took about 10 minutes.
Preheat the oven to 350 degrees.
Allow the potatoes to cool for 5 minutes, or until you are able to handle them. Slice the very top off of the potato. Scoop out the insides of the potatoes, being careful not to break the skin. Leave about 1/4" of potato on the skin so that it can hold the filling. Place the scooped potato in a bowl.
Add the drained tuna, condensed soup, 1/2 cup cheddar cheese and salt, if desired. Mix well.
Spoon this mixture back into the potatoes and top with the remaining cheddar cheese.
Bake the potatoes on a baking sheet at 350 degrees for 10 minutes, or until the cheddar cheese is melted. If you'd like the cheddar cheese browned a little bit, place the baking sheet under the broiler for 2-3 minutes on low. Watch carefully!
Sprinkle with fresh parsley for serving.
You can add more tuna or more cheddar cheese if you'd like. If you have any extra filling that doesn't fit in the potatoes, bake it in a small baking dish that has been lightly sprayed with cooking spray.