Soak the capers in a bowl of water. Squeeze all the lemon juice into a large shallow bowl and add 4 tablespoons of oil. Peel the garlic and finely chop with the chilli, anchovies, pistachios, drained capers and mint leaves. Scrape it all into the bowl and mix together well.
Reserving the tentacles, run a sharp knife down the length of each squid tube, cutting through one side only so you can open each one out like a book. Lightly score the inside of each tube in a criss-cross fashion at ½cm intervals. To cook the squid, follow Franchina’s guidance and get the tentacles on early, then add the tubes, from largest to smallest. In a screaming hot griddle pan or on a barbecue, cook each piece for about 1 minute per side – with no oil or seasoning – until lightly charred and starting to curl. Start with the cut side when you do the tubes, and keep the squid moving for even cooking. As each piece is done, use tongs to dunk it straight into the salsa, turning and coating it in all that flavour.
Slice the tomatoes and lay over a serving platter. Finely slice the squid tubes, pull the tentacles apart, then arrange on top of the tomatoes. Spoon over all the remaining salsa, and serve hot or at room temperature.