Not actually barbacoa.

Perfect for tacos, burritos, quesadillas, whatever.

3 lb chuck roast
1 tsp cumin
1 tsp chili powder
1 (or 2 if you like it hotter) sliced jalapeño pepper
1-2 bay leaf
1 tsp minced garlic
1 Tbs oregano
1 sliced small/medium red onion
1 tsp (or 2 again) Chipotle Tabasco sauce
1 tsp lime juice
1/4 cup apple cider vinegar
2 cups chicken stock or broth
salt and pepper and garlic powder*

You can literally just put all of this in your slow cooker and ignore it 8 to 10 hours until it falls apart.

But I have some suggestions:

Trim any excessive fat from the roast (but not all.) Season with salt, pepper, and garlic, on both sides. Brown the edges on high heat on the stove. Great searing tips here.

Caramelize the onions peppers in an oiled pan on medium heat with salt and pepper as well to bring out flavors. If you splash some broth on pan to deglaze it, you can get all the yummy char bits into the slow cooker as well.
You can also substitute just about any meat for this. It's equally wonderful with chicken.

Cook this with boneless skinless chicken thighs, and you can add splash of V8, a dollop of sour cream, and sprinkle some tortilla chips and shredded cheddar on top and you've yourself a soup too.

Cook on low for about 8 to 10 hours, OR high for 4 to 5. Around the 7 or 3 hour mark, it should easily shred with a fork. I usually tear mine up right in the pot around then and let it cook for another hour or so.

This last round, I covered the roast with extra broth completely and saved the liquid. Makes for a great spicy au jus, gravy base, dip for quesadillas, etc. and since I had so much, I will probably just use it as a low maintenance broth for my next spicy roast or beef soup. Freezes into a great meat jelly for next round! If you have leftover meat from cooking it either way, freeze the meat and broth together saves great.

Update: Reusing the broth was a total success!

*2 parts salt
1 part black pepper
1 part garlic powder

Mix together in a container, easy in a pinch. I stole this from Paula Deen, but doubled up on the garlic and pepper. Whatever.