To make black bean and corn relish. Combine black beans, corn, red onion and red bell pepper. Pour over vinegar, squeeze the juice of 1/2 of a lime, season with salt and pepper and allow to sit for a half an hour or up to one day.
For the salad dressing. Combine sour cream, salsa, the juice of half a lime, chile powder, cumin and salt and pepper. Stir to combine. Every salsa is a little different so you may need to add more salsa or add more sour cream to reach the desired consistency for your dressing. Adjust seasonings with salt and pepper.
For the main salad. Chop up romaine lettuce. Add avocado, black bean and corn relish, cheese and cilantro. Pour over dressing and toss to combine. Garnish the top with more shredded cheese and cilantro. Serve with cut up slices of lime and tortilla chips.