Place pork, onion, and seasonings into a 6-quart slow cooker. Mix to coat meat in seasonings.
2. Step
Add ketchup and mustard, spreading evenly over the outside of the meat.
3. Step
Set slow cooker to High and cook for 4 hours, until the meat pulls apart easily. Alternatively, the meat can be cooked on the Low setting for 8 hours.
4. Step
Remove meat from slow cooker and transfer it to a bowl or cutting board. Using two forks, shred the meat into bite-sized pieces.
5. Step
Preheat oven to 400˚F (200˚C).
6. Step
Using a cast-iron pan or other oven-safe dish, assemble the nachos layer by layer. Chips, then pork, onion, BBQ sauce, and cheese. Repeat as desired for additional layers.
7. Step
Bake for 8-10 minutes until cheese is melted and bubbling.
