Place the sweetbreads in a large bowl and cover with cold water. Soak for at least 1 hour, then drain.
Transfer to a pot, cover with fresh water, add salt and vinegar, and simmer for 10 minutes until firm and pale.
Remove and place in cold water to stop cooking.
Peel off the outer membrane and trim any tough parts.
Cut the sweetbreads into bite-sized pieces.
Heat oil or butter in a skillet over medium heat.
Add garlic and cook until fragrant.
Add sweetbreads and cook in a single layer.
Turn occasionally until golden brown and crispy (about 10–15 minutes).
Season with salt and pepper.
Drizzle with lemon or lime juice.
Warm tortillas in a skillet.
Assemble tacos with sweetbreads, onion, cilantro, and salsa. Serve immediately.
