For the pickled onion, place the onion, vinegar, sugar and a pinch of salt in a bowl and using you hand press the onions together to macerate. Let stand for 15 minute or until ready to use.
Pre heat the grill element in the oven, brush the corn with a little olive oil and season with salt. Grill on all sides until charred. Once cool enough to handle, cut the kernels off.
Combine the tuna slices with the zest of the lime, salt and a teaspoon of the olive oil.
For the avocado puree, blend or mash the avocado with lime juice, tobasco (as much or as little as you like), salt and pepper until smooth.
Heat a shallow amount of the vegetable oil to 180°C in a pan and cook the tortillas one at a time for 1 minute on each until crisp. Drain on paper towel.
To serve spread avocado puree on to the crisp tortillas. Portion tuna between each crisp tortilla and top with corn and drain pickled onions that have been drained from the pickling liquid.