Cut avocados in half, lengthwise. To remove the pit, strike it swiftly with a knife, twist and remove.
Drain the can of tuna and dress with the juice of one lemon, olive oil and a sprinkle of black pepper.
Wash lettuce leaves and pat dry. Slice the tomato into 8 rounds. Peel the eggs and cut each one into quarters.
Scoop 1/4 of the tuna into each avocado half.
Slice the remaining lemon into thin slices for garnish. Arrange each avocado half on a plate with 2 lettuce leaves, two tomato rounds, two egg quarters, and a few slices of lemon.