Prepare cornbread mix according to package directions, adding chiles. Cool and crumble.
Process light mayonnaise and next 4 ingredients in a food processor or blender until smooth, stopping to scrape down sides.
Layer a 4-quart bowl with half of shredded lettuce, half of crumbled cornbread, one-third of mayonnaise mixture, and half each of black beans, corn, shredded Cheddar cheese, and next 3 ingredients. Repeat layers. Top with remaining mayonnaise mixture. Cover and chill 1 to 2 hours. Garnish, if desired.
Note: Don't forget to buy the other ingredients that you'll need to make the cornbread.