I think of this recipe as an inside-out tuna sandwich: a halved head of iceberg lettuce becomes two bowls for the tuna salad, which then gets topped with crisp toast points and, if you're feeling fancy, a poached egg. Using the water that the tuna is packed in for the dressing adds extra flavor—and turns this into a no-waste dish!
Cut the head of lettuce in half. Using a large spoon, hollow out the center of each half to create a bowl with walls that are about 1 inch thick. If the lettuce "bowl" is a little wobbly, then slice off a sliver from the rounded bottom to create a flat surface. Shred all of the lettuce that has been removed and set aside.
Place the tuna in a medium bowl and break it up into smaller chunks with a fork. Add the pickles, parsley, scallions and shredded lettuce, and toss together so that all the ingredients are evenly distributed.
In a small bowl, whisk together the mayonnaise, 2 tablespoons of the reserved tuna water (plus more if the dressing is too thick) and hot sauce. Season with salt and pepper. Add to the tuna and toss well until evenly coated. Divide the mixture between the prepared lettuce bowls, mounding into the center of each.
Poach the eggs: Crack each egg into separate small bowls. Bring 2 inches of water to a simmer in a medium saucepan over medium heat. Gently tip each egg into the simmering water and cook for 2 minutes, then remove from the heat and leave the eggs in the hot water until set, about 8 minutes. Remove each egg with a slotted spoon and drain in the spoon over a paper towel to remove any excess water.
Lightly butter the toasts and cut each in half diagonally. Arrange the toast points on top of the tuna salad and then place the poached egg on top of the toast points. Sprinkle a little salt and pepper over each egg. Serve immediately.