For the croquettes, melt the butter in a medium saucepan over a medium heat, add the ham and leave to cook gently for a minute or two to soften.
Stir in 110g/4oz of the flour and cook for one minute, then very gradually stir in the milk, a little at a time, beating really well between each addition so that the mixture becomes silky smooth.
Increase the heat slightly, bring to the boil, and leave to cook gently, whisking constantly, for five minutes, to cook out the flour.
Stir in the chicken and one teaspoon of salt, or to taste, then stir in the hard-boiled egg.
Scrape the mixture into a bowl, press a sheet of cling film onto the surface, and chill in the fridge, for at least six hours but ideally overnight, until really firm.
When you are ready to make the croquettes, lightly flour the palms of your hands and for each croquette shape 1½ tablespoons of the chilled mixture into a ball, and then roll into a cork-shaped barrel. You should make about 24 croquettes. Refrigerate again for 30 minutes.
Meanwhile for the salad, remove and discard the outer leaves of the lettuce if necessary. Break the remainder into approximately 7cm/3in pieces, wash and dry well, in a salad spinner if you have one.
Spread the leaves over four medium-sized plates and arrange the tomatoes, onion and asparagus on top.
Scatter the flaked tuna over the centre of each plate.
Whisk the red wine vinegar and olive oil together with the salt to taste and drizzle over the salads.
Garnish with the hard-boiled eggs and green olives.
Heat some oil for deep-frying to 190C/375F. (Caution: hot oil can be dangerous. Never leave unattended.)
Put the remaining 75g/3oz flour, egg and breadcrumbs into three separate shallow trays or bowls.
Take the croquettes from the fridge and dip them four or five at a time into the flour, then the beaten egg and then the breadcrumbs. Lower them into the hot oil and cook for not quite two minutes until crisp and lightly golden-brown. You can tell when they are done because as they cook they begin to make a different noise in the fryer.
Lift out with a slotted spoon and set aside on plenty of kitchen paper to drain briefly. Serve while they are still hot.
To serve, pile the hot croquettes straight onto a plate with a spoonful of salad alongside.