Pierce the potatoes all over with a fork. Rub each potato with 1/2 tsp. olive oil and season each with 1/8 tsp. of the salt; set aside.
Heat the remaining 1 tablespoon oil in a large skillet over medium-high. Add beef, season with 1 tsp. each salt and pepper, and cook until browned.
Place meat in slow cooker. Add tomato sauce, onion, broth, garlic, and taco seasoning. Stir well.
Place a piece of parchment paper or aluminum foil on top of the beef mixture. Place the potatoes on top of the parchment in a single layer.
Cover and cook on the LOW setting until the potatoes are tender, 7 to 8 hours.
Remove the potatoes from the slow cooker and remove and discard the parchment or foil. When cool enough to handle, cut potatoes in half lengthwise down the center without cutting all the way through. Use a fork to fluff the inside of the potatoes. Place the potatoes on plates.
Stir the beef mixture and spoon it over each potato. Top with shredded cheese, lettuce, tomato, and sour cream as desired.