Using a large bowl, add beef, salt, cumin, oregano and allspice. Toss until well coated, pressing the spices lightly into the beef. Wrap in plastic wrap and refrigerate overnight.

Using a large skillet, add oil and place over medium-high heat. Once hot, add beef and cook for ~30 seconds per side, or until browned. Transfer beef into slow cooker.

Using a blender, add chipotle peppers, adobo sauce, broth, apple cider vinegar, tomato paste, lime juice, garlic, onion, cayenne pepper, black pepper; process until smooth. Pour mixture over beef in slow cooker; stir until beef is well coated.

Cook on low for 6-8 hours, or until beef is fork-tender. Shred beef using 2 forks.

Brush the poblano peppers with oil and place on sheet pan. Broil on high for 8-12 minutes, or until skin becomes well-charred. (Note: Keep a close eye on the peppers at this stage. Different broilers cook at different rates! You’re looking for the skins to blister and bubble.)

Allow peppers to cool slightly, then peel and discard the charred skin. Dice and set aside. (Note: ensure that all of the seeds are removed from the peppers.)

Cook frozen corn according to package directions; set corn aside. (Note: Fresh corn can be substituted here if available.)

Using a medium bowl, combine the diced poblanos and corn with all remaining ingredients (onion, jalapeno, cilantro, lime juice, salt, and pepper).

Using a medium saucepan, add butter and heat over low heat until melted.

Add the rice and lime juice; continue cooking, stirring often, for 1-2 minutes.

Add water and salt; stir gently and increase heat to medium-high. Once water begins to boil, cover and remove pan from heat. Do not uncover or stir again.

Allow rice to rest until all of the water is absorbed (~18-20 minutes).

Once rice is cooked, add the chopped cilantro and fluff rice with a fork.

Layer rice and lettuce in a bowl.

Add barbacoa, guacamole, corn salsa, shredded cheese, sour cream, and any additional toppings of your choice.

{Optional} Serve with warm flour tortillas.