Place brisket in a Dutch oven with onion, garlic powder, cumin, oregano, chili powder, salt and pepper.
Add enough water to cover brisket. Cover and bring to a boil over high heat.
Reduce to a simmer and let do its thing for about 4 hours, until meat easily pulls apart.
Carefully remove beef from Dutch oven and place in a bowl. Shred with two forks, cover and set aside. Discard liquid and onion.
Puree the chipotle peppers in a food processor.
Toss the olive oil, vinegar, chipotle peppers, lime juice, tomatoes, and radishes together. Add meat and toss to combine. Season with salt and pepper as needed.
Cover and refrigerate at least 2 hours before serving. Toss again before serving and check for seasoning.
Serve over shredded lettuce with warmed tortillas and additional toppings as desired, such as queso fresco, pickled onions, diced tomatoes.
Notes
This dish is normally served with radishes and avocados garnishing the plate. When plating this I discovered that every single one of my avocados had gone bad. I was very sad for it was a sizable bag of avocados.