01 - Combine apple cider vinegar, water, sugar, and salt in a small saucepan. Bring to a boil, stirring to dissolve sugar and salt. Place sliced onions in a heatproof jar or bowl; pour hot liquid over them. Let sit at room temperature for at least 20 minutes.
02 - Heat olive oil in a large skillet over medium heat. Add chopped onion and cook until softened, about 2 to 3 minutes. Add minced garlic and cook for 30 seconds.
03 - Add ground beef to the skillet, breaking it apart with a spoon. Cook until fully browned, approximately 5 to 7 minutes. Drain excess fat if necessary.
04 - Incorporate ground cumin, smoked paprika, chili powder, dried oregano, salt, and black pepper. Stir in beef broth or water. Simmer for 3 to 5 minutes until most liquid evaporates and flavors combine.
05 - Heat tortillas in a dry skillet or microwave until flexible and warm.
06 - Fill each warmed tortilla with seasoned beef, then top with shredded lettuce, diced tomatoes, pickled onions (drained), crumbled cheese, and fresh cilantro. Serve with lime wedges.