Combine diced onions, tomatoes, salt and lime juice in a non-reactive bowl and let it sit about 5 minutes.
Combine the remaining ingredients in a large bowl, taste for salt and adjust as needed.
Refrigerate and let the flavors combine at least an hour before serving.
NOTE: The terms "reactive" and "nonreactive" are referring to the type of metal from which your pot or bowl is made. Aluminum, cast iron, and copper are all "reactive." Stainless steel, ceramic, glass and metal cookware with enamel coating are all "nonreactive."