Place all the ingredients for the vinaigrette in a blender and puree until smooth. You may make the vinaigrette up to a week ahead and store covered in the refrigerator. If made ahead, whisk with a fork or whisk to re-emulsify prior to using. You may also shake it in the covered container.
In a large mixing bowl, combine black beans, garbanzo beans, corn, red bell pepper and red onion. Pour vinaigrette and combine well. Add hearts of palm, gently toss and serve.