Preheat your oven to 400°F.
Prepare a baking sheet by lining it with parchment paper. Pierce each potato several times with a fork, then brush them thoroughly with vegetable oil.
Place the potatoes on the baking sheet and bake in the preheated oven for 1 hour, or until they’re tender.
While the potatoes are baking, cook the ground beef and chopped onion in a large skillet over medium heat until the meat is fully browned.
Once the beef is cooked, mix in the taco seasoning, water, and diced tomatoes with green chilies. Let the mixture simmer for 10 minutes, until the sauce thickens. Remove the skillet from heat.
When the potatoes are done, take them out of the oven and cut each one in half lengthwise.
Scoop out the inside of each potato, leaving a thin layer of flesh attached to the skin.
Cut each potato half in half again to create four quarters.
Fill each potato skin with the taco meat and top with shredded cheese.
Place the loaded potato skins back on the baking sheet and return to the oven for 15 minutes, or until the cheese is melted and the skins are crispy.