The red onions, cilantro, and lime juice are all ingredients that taste great when served fresh. Due to the excess amount of ingredients that only taste great when they are used straight from the supermarket, we recommend you prep this salad only a couple of minutes or hours before it is to be served. You can always freeze the cooked-sweet corn on its own, however, and mix in the dressing whenever you feel like having a bowl of this Mexican salad.