Bring an inch of water to a rolling boil in a small sauce pan. Gently lower an egg in the water, cover the pot, and adjust the burner to keep that rolling boil going. Cook the egg for 11 minutes, then drain and peel the egg immediately under cool running water.
Open and drain the tuna cans. Place the tuna in a whatever airtight container you plan to store it in.
Use the egg slicer to slice the egg in two directions — slice it horizontally, then rotate and slice it vertically. Add the chopped egg to the tuna.
Add the rest of the ingredients to the tuna and egg and mix well with a fork, mashing the egg yolk and breaking up the bigger chunks of tuna. Taste and adjust seasonings accordingly. You may want more mayo or less mayo, more salt and pepper, more crunchy bits, etc. Adjust, adjust, adjust!
Cover and let sit in the fridge overnight, ideally 12-18 hours, before serving.