Prepare the Tuna Tartare. Begin by finely dicing the fresh tuna into small cubes. Place the diced tuna in a mixing bowl and add the olive oil, lemon juice, salt, pepper, and garlic mayo. Mix well and let it sit for about half an hour so that the flavors of the marinade nicely infuse the tuna.
Cook the pasta according to the package instructions or until it is desirably tender. Drain and set aside to cool.
Once the cooked pasta has cooled down, add it to the tuna tartare mixture. Gently toss or fold with a spatula to ensure that the pasta is well coated with the sauce and the tuna is evenly distributed throughout the mixture.
Add the cherry tomatoes, pickles, olives, and sweet corn. Repeat the tossing and folding until all the ingredients are fully incorporated.
Taste and adjust the seasoning by adding more salt, pepper, or lemon juice if required.
Garnish with parsley and refrigerate for a few hours.
Serve cold, and drizzle some thousand island dressing on top (optional).