Melt butter in a saucepan, add ham, and cook for two minutes to soften.
Stir in 110g of flour for one minute, then gradually whisk in milk until smooth.
Boil and whisk the mixture for five minutes to cook out the flour.
Stir in the chicken, salt, and chopped hard-boiled egg.
Place mixture in a bowl, cover with cling film, and chill for six hours or overnight.
Shape 1½ tablespoons of mixture into barrel shapes and refrigerate for 30 minutes.
Prepare the lettuce by breaking it into 7cm pieces, then wash and dry.
Arrange lettuce, tomatoes, onion, and asparagus on four plates.
Scatter the flaked tuna over the center of each salad.
Whisk vinegar, olive oil, and salt together and drizzle over the salads.
Garnish salads with quartered hard-boiled eggs and green olives.
Heat deep-frying oil to 190°C.
Set up three trays containing 75g flour, beaten egg, and breadcrumbs respectively.
Coat croquettes in flour, then egg, then breadcrumbs, and fry for two minutes until golden.
Drain croquettes on kitchen paper briefly.
Serve hot croquettes immediately alongside the prepared salad.