Measure sour cream in a mixing bowl. Keep at room temperature.
Microwave the frozen corn to thaw and gently squeeze the moisture out of it.
Chop up half an avacado into a very tiny dice, about 1/2 a cup.
Drain the preserving liquid from the chilies and do a quick rinse in running water. Then gently squeeze out any liquid from the chilies.
Chop the scallions very finely
Combine the above 5 ingrdients. Now add 1 and 1/4 teaspoon of taco seasoning and mix well, add salt if necessary. Spread onto a shallow serving bowl that can go into the oven.
Crush the fried onions roughly. Mix the Jack cheese. Add the remaining 1/4 teaspoon of Taco seasoning.
If using lime zest, run the lime a couple of times back and forth on a microplane. Scrape the oils and the zest[ a little goes a long way] and add to the onion cheese mixture. Mix to incorporate well and spread over the dip.
Turn te broiler to medium and put the dip in the centre of the oven and broil fo 5 minutes or so till the cheese melts and the fried onions turn a golden brow, Turn the broiler off and keep the dip warm. Serve with vegetable crudites and tortilla chips.