Cut the potatoes into bite-sized pieces that are 3/4 inch (2 cm) thick, add the chopped potatoes into a stockpot, all in a flat layer, then fill with water just enough to cover the potatoes, season generously with salt, and heat with a high heat

In the meantime, add the eggs into a saucepan, fill with water just enough to cover the eggs, and heat with a high heat, when it comes to a boil, place a lid on the pan, and turn off the heat, let the eggs sit for 10 to 11 minutes to end up with perfectly hard-boiled eggs

About 15 to 20 minutes after turning on the heat on the potatoes they should be cooked through, you want them al dente, otherwise they wil break apart (you can always pierce them with a toothpick to ensure they are done), remove the stockpot from the heat, drain the potatoes into a colander and rinse under cold water

Drain the can of tuna into a fine sieve with a bowl underneath and gently flake the tuna, cut the onion into small slivers, and roughly chop the hard-boiled eggs

To make the dressing, add the olive oil into a bowl, along with the sherry vinegar, grated garlic, chopped parsley, and season with salt & pepper, whisk together

Add the potatoes back into the stockpot (you can also use a large bowl), along with the drained canned tuna, chopped hard-boiled eggs, sliced onion, sliced green olives, and dressing, then season with salt & pepper and gently mix together until well mixed

Serve at room temperature or even chilled, as it will hold for up to 3 to 4 days in the fridge, enjoy!