Shredded Beef: In medium bowl, season beef with Adobo seasoning. In high-sided medium Dutch oven or skillet set over medium heat, add olive oil. Add seasoned beef to Dutch oven and sear, turning cubes once, for 4 to 6 minutes or until starting to brown; transfer to plate.
Reduce Dutch oven to medium heat. Add onion, garlic and cumin and cook, stirring occasionally, for 3 to 5 minutes or until onion is starting to soften. Stir in 1 cup water, tomato sauce, chipotle peppers and adobo sauce; bring to a boil.
Return beef and drippings to Dutch oven. Reduce heat to low. Cover and cook, stirring occasionally, for 2 to 2 1/2 hours or until beef is very tender. Using a slotted spoon, transfer beef to cutting board. Use two forks to shred meat; transfer beef and juices back to sauce; set aside.
Creamy Avocado-Cilantro Sauce: Meanwhile, in blender, add avocado, sour cream, cilantro, lime juice, garlic and adobo seasoning; purée until blended and smooth. Refrigerate until ready to serve.
Flautas: Preheat oven to 275°F. In high-sided medium skillet set over medium-high heat, add vegetable oil and heat until hot but not smoking. Fry tortillas, one at a time, submerging in oil for 5 seconds or until soft and pliable but not crisp; drain on paper towel–lined baking sheet (do not discard oil).
Assembly: Spoon 2 tbsp. beef filling into center of each tortilla; roll tightly to enclose filling like a cigar. Secure seam-side with 2 toothpicks. Repeat with remaining tortillas, beef filling and toothpicks.
Reheat the oil-filled high-sided medium skillet over medium heat. In batches to avoid crowding, fry flautas seam-side down in oil, cooking, turning once, for 4 to 6 minutes or until golden brown and crispy all over. Transfer to parchment paper–lined baking sheet and keep warm in preheated oven until all are cooked. Remove toothpicks.
Divide shredded lettuce among 4 to 6 plates. Top with flautas and garnish with Pico de Gallo Salsa, avocado sauce, queso fresco and cilantro.
Note: Substitute beef brisket or chuck roast for the beef blade roast.