1. Preheat oven to 400ºF. Spread tortilla wedges on 1 or 2 large, ungreased baking sheets and bake until crisp, 10 to 15 minutes.
2. Cut kernels off ears of corn into a large bowl (you should have about 1 1/2 cups). Add beans, avocado, tomatoes, scallions, cumin, olive oil, lime juice and shrimp and toss gently to combine. Season with salt and pepper.
3. Arrange lettuce on a serving plate, spoon shrimp salad on top and serve with tortilla wedges.