1. Make sauce for beef: Wipe chiles clean with a damp cloth, stem and seed, and tear into pieces. Heat 1 tbsp. oil in a heavy medium saucepan over medium heat. Sauté onion and garlic until softened, 1 to 2 minutes. Add chiles and cook, stirring, until fragrant, 1 to 2 minutes. Add 1 1/2 cups water, the cumin, tomatoes, oregano, and 1 tsp. salt. Bring to a boil, then reduce heat and simmer, covered, until chiles are softened, about 10 minutes. Purée sauce in a blender until very smooth.
2. Meanwhile, season beef with the remaining tsp. salt. Heat the remaining tbsp. oil in a 5- to 6-qt. pot over medium-high heat. Brown beef, turning occasionally, 10 to 14 minutes. Discard fat, if any.
3. Pour sauce into pot and add bay leaf, cola, and a little water if needed to barely cover meat. Cover, reduce heat, and simmer until beef is very tender, 3 hours.
4. With a slotted spoon, transfer beef to a plate. Let cool slightly, then tear into shreds, discarding any fat or gristle. Meanwhile, boil sauce over medium-high heat, stirring occasionally, until slightly thickened and reduced to about 3 cups, 10 to 30 minutes. Stir in beef and heat a few minutes until hot. Remove bay leaf.
5. Make tacos: With a slotted spoon, transfer beef with some sauce to a bowl. Spoon beef into tortillas (double tortillas if they're thin), tuck in accompaniments, and serve with remaining sauce if you like.
*Find in the Latino foods aisle or spice aisle of a supermarket, or at a Latino market.
Make ahead: Through step 3; chill, covered, up to 2 days.
Note: Nutritional analysis is per serving.