Place the eggs in a pot and submerge under water. Set the heat on high and let the water boil. Once it's boiled turn the heat off and cover the pot with a lid for about 16 minutes. Then rinse with cold water.
In a bowl combine the tuna, chopped egg, chopped onion, mayonnaise, salt, and black pepper.
Spread mayonnaise on 2 slices of toasted bread. Then add the tuna mixture, lettuce, tomato, and the top bread slice.