Start by grating the mild cheddar, sharp cheddar, and processed cheese into a large bowl.
Add the diced pimentos to the cheese mixture, ensuring even distribution for that tangy flavor.
Incorporate mayonnaise into the bowl gradually.
Stir thoroughly until smooth and creamy.
Sprinkle in the minced green onions and, if using, add the toasted pecans for a crunchy texture contrast.
Chill the mixture in the refrigerator for at least an hour before serving.
This will help the flavors marry and intensify.