3 tbsp olive oil (use what you can from the tins of tuna)
15g parsley, roughly chopped
½ lemon juice
Put the onion, celery, capers and tuna in the centre of a large chopping board and roughly chop everything into even-sized pieces.
Mix all of the dressing ingredients in a small bowl until combined.
Tip the chopped mixture into a large mixing bowl followed by the drained beans. Pour in the dressing, season well with cracked black pepper and toss everything to combine (check for seasoning - keeping in mind the capers + beans will add salt)