Combine all the spice rub ingredients in a small bowl. Generously rub all over the chuck roast steak. Place in the bottom of a slow cooker, top with the diced peppers and onions. Cover and cook on LOW for 6 to 8 hours.
For The Pico de Gallo
Combine the Avocado Pico de Gallo ingredients in a bowl, and gently stir to combine. Cover and place in fridge until ready to use.
Once beef is tender, use two forks to shred the steak (should fall apart very easily).
Assemble Nachos:
Place a pile of tortilla chips on a plate, cover with the hot carne asada, some shredded cheese, a nice helping of avocado pico, and some sour cream.If desired, you can pop the nachos under the broiler in your oven to melt the cheese more.