1. Place vinegar, sugar, salt, and red onion into medium bowl and toss to combine. Set aside. 2. Heat a medium cast-iron or nonstick skillet over medium-high heat. Working one at a time, heat tortillas, 10–15 seconds. Flip and heat on second side, about 10 seconds. Stack and wrap in a kitchen towel to keep warm as you go. (Tortillas can also be warmed in a foil packet in oven). 3. Heat oil in small skillet over medium heat. Add pork and sauté until heated through and beginning to brown, about 3 minutes. Add taco sauce and toss to coat meat. Remove from heat and set aside. 4. Assemble tacos: Divide meat evenly between tortillas and top with marinated red onion, avocados, chopped tomatoes or salsa, jalapeños, cilantro sprigs, and cheese. Serve with lime wedges alongside.