For the meat: Rub the flank steak with oregano, cumin, salt and cracked pepper. Place the steak, beef stock, water, garlic, onion, bay leaves and peppercorns in a large pot, bring to a boil. Simmer for 1 1/2 hours until meat is fork tender and comes easily apart with a fork. If you need to add some more liquid during the cooking process, go ahead. Add more beef broth or water would be fine. Remove the pot off the burner and allow to cool to room temperature, about 20 minutes.
When it's cooled to room temperature, cover with lid and place into the refrigerator. Cool in the refrigerator for 1 to 3 hours. After it's cold, trim off any remaining fat, cut into 4 pieces across the grain and then shred using 2 forks.
Place it back into the liquid until ready to serve. Before adding to the salad, drain off liquid and discard.
For the vinaigrette: Whisk all the ingredients together, adding in the olive oil in a steady stream until incorporated.
For the salad and assembly: Toss the lettuce and vegetables with the vinaigrette, and top with meat. Add freshly made corn tortilla chips around side of bowl.