Preheat sous-vide to 170. Or, if using dutch oven, preheat water or broth sufficient to cover tongue to roughly 170.
Rinse tongue, pat dry, rub with oil, salt, and pepper.
Add tongue, onion chunks, tomato chunks, and cilantro to vacuum bag. If using dutch oven method, add all directly to broth.
Submerge tongue and cook for 24 hours.
Remove tongue and reserve juices from the bag.
Set drained bag in an ice bath for 15 minutes.
Remove the membrane from the tongue.
Dice tongue into 1/2 inch chunks.
Add chipotle peppers and lime to half reserved liquid, blend, and add salt to taste.
Sauté diced onions in remaining liquid and add tongue. Cook down until the meat begins to crisp up. Feel free to add some of the chipotle sauce to this final cooking, or just add to tacos as you are making them.
Toast your tortillas.
Add your favorite taco toppings and fiesta!