Dice the onions and place them in a bowl with cold water (this helps to reduce their bite). Dice the tomatoes and chop the cilantro. Drain and rinse the corn and black beans. After a minimum of 10 minutes, drain the onions.
Add all of the ingredients to a large mixing bowl and stir to combine. Taste and adjust the seasonings as needed.
Refrigerate for at least one hour, for best flavor.
Serve with tortilla chips.
Notes
LeftoversStore leftovers in an airtight container in the refrigerator for up to 4 days.