Step 3: Spread a thin layer of mayonnaise on one side of each slice of sourdough bread.
Step 4: Heat up the cast iron skillet. Place two slices of sourdough mayonnaise side down on the cast iron. The mayonnaise will help evenly toast the bread.
Step 7: Spoon the tuna mixture evenly on top of the sprouts.
Step 8: Place the cheese on top of the tuna mixture. Top the cheese with the other half of sourdough.