Sandwich with tuna and avocado

Products:
4 slices of bread
120 g sandwich tuna
lemon juice
1/3 avocado
salt, pepper
1 big tomato
a few slices of red onion
butter
boiled egg

Preparation:
Take one of the slices and grease it with a little butter. Boil avocado and smear it on bread like a paste.

Put on it two finely chopped tomatoes, red onions, or finely chopped, and tuna. Season with lemon juice, pepper, salt and put the second slices. Optionally, add a boiled egg.