This is a nice appetizer - easy and impressive.  Use thick, crisp chips for scooping.  After serving discard any uneaten dip.

1/4 cup fresh lime juice
1/4 cup chopped fresh cilantro
2 tablespoons olive oil
4 teaspoons minced canned chipotle chiles **I use canned green chiles tossed in 1/2 teaspoon chipotle spice (now available in spice section of your supermarkets)
1 tablespoon red wine vinegar
1 teaspoon ground cumin
2  15-16 ounce cans black beans, rinsed & drained
1 1/2  cups frozen corn kernels
1 1/2  cups chopped red onion
1 1/2  cups chopped tomatoes (about 3 medium)
1 cup chopped green bell peeper
1 large ripe avocado, pitted, peeled and diced chips

Whisk first 6 ingredients in a large bowl to blend.   Stir in beans, corn, onion, tomatoes, and bell pepper.  Mix in avocado;   season to taste with salt and pepper.   Can be prepared 2 hours ahead.  Cover and refrigerate.