Preheat the oven to 425 degrees F. Scrub the potatoes clean, pat them dry then rub with olive oil. Poke holes all over with a fork. Sprinkle with kosher salt and pepper.
Bake the potatoes for 60 to 90 minutes, or until they are fork tender.
While the potatoes are baking, heat the olive oil in a skillet over medium heat. Add the mushrooms and the garlic. Cook until the mushrooms are soft and juicy, about 5 minutes. Sprinkle with salt and pepper. Transfer the mushrooms to a plate.
Place the ground beef in the same skillet over medium heat. Season all over with salt and pepper. Cook until browned and crisp, breaking it apart with a wooden spoon or meat chopper. Stir in the dijon mustard. Add the mushrooms back into the pan with the beef and stir. Add a sprinkle of the cheese and stir.
Once the potatoes are done, slice them open up top and gently pull them apart. Fill each potato with the ground beef/mushroom mixture. Drizzle with the dijon sauce, then top with the cheese. Repeat with remaining potatoes.
Place the potatoes back into the oven for 10 minutes so the cheese can melt. Remove and drizzle with more dijon sauce and top with green onions. Serve!