In a smaller pot, bring eggs to boil on high, then lower heat and let boil for 15 minutes. Meanwhile, peel potatoes and place in another pot. Bring potatoes to boil on high, lower the temperature and check to see whether they're done. Potatoes are ready when you can stab them with a fork easily but they are not falling apart. Finally, bring corn kennels to a boil in another small pot and remove from heat.
Drain eggs, potatoes and corn. Peel and cut eggs into rounds the thickness of 2-3 pennies stacked together. Cut potatoes into rounds the same way as eggs. Mince onion.
Dice the tomato, mince parsley, combine and leave aside for the top of the salad.
Make the dressing by combining all ingredients and whisking them well.
Take a large bowl and start layering your salad. You should have a total of two to three layers of everything. Start with potato rounds, add tuna, then eggs, corn, and onion. Then top it generously with the dressing. Repeat once or twice, depending on how many ingredients you have left. Top each layer with the dressing.
Once you are finished add the tomatoes and parsley on top.
Keep in the fridge until you are ready to eat it, and eat it the same day.
If you opt for lettuce, start with it as the first layer. Make sure to chop it up so it doesn't take over the bowl.