Place the pork tenderloin in a slow cooker and cover with 1 cup of water. Cook on high for 3 to 4 hours or on low for 6 to 8 hours.
When the pork is cooked and tender, use forks to shred the meat in the slow cooker. Cover and reduce the heat to medium until ready to serve.
While the pork is cooking, place thinly sliced onions into a glass jar.
Combine 1/2 cup water, 1/2 cup apple cider vinegar, kosher salt, sugar and peppercorns in a small saucepan. Simmer for 2 to 3 minutes.
Pour the vinegar mixture over the onions. Allow to cool, then seal the jar and refrigerate until ready to serve.
Place tortilla chips on a plate and top with shredded pork.
Drizzle with melted queso cheese dip and garnish with pickled red onions, pico de gallo and sour cream.