1. Warm your oven to 400°F. Clean and dry the potatoes, then brush each one with olive oil and make several holes with a fork. Place on a sheet pan and cook for 50 minutes to an hour, or until they're nice and soft. Take them out of the oven and let them cool a bit so you can handle them.
2. Change the oven temp to 425°F. Slice each potato in half lengthwise and scoop out the center so that there's about ½ inch around each edge. You can scoop out less if you want more potato in each bite and less crispiness overall. Brush each potato half lightly with olive oil inside and out, and season with salt and pepper. Put them face down on a parchment-lined sheet pan and cook for 10-15 minutes, then flip and cook for another 10-15 minutes, depending on how crispy you want them.
3. While the potato skins are cooking, heat a tablespoon of olive oil over medium-high heat. Add the diced onion and cook for about 3-4 minutes, or until they're translucent. Add the ground sirloin and brown, breaking it up into chunks. When the meat is browned, drain any extra grease and put it back in the pan.
4. Mix in the ketchup, mustard, Worcestershire sauce, garlic, salt, and pepper. Add one cup of the shredded cheddar and stir until melted.
5. Put the cheeseburger mixture (about 1 ½ tablespoons) into each potato skin and top with the rest of the shredded cheese. Bake for another 3-5 minutes, or until the cheese is melted.
6. Take the potatoes out of the oven and let them cool for a few minutes before putting them on a serving platter. Add your favorite toppings and enjoy!