Combine all the brine ingredients in a small sauce pan and heat until just dissolved.
Pour over the spring onion whites and chill for at least a few hours.
Slice the greens into 1-2 inch pieces, place on a sheet pan and bake in your oven at the lowest possible temp (I did 125 in my countertop toaster/ convection oven) for 8 or so hours, until all moisture has been evaporated and they are dry and crispy.
Weigh the dehydrated greens then place in a spice grinder along with equal parts salt. Blitz to a fine powder.
Add the tuna, olives, dates, pickled spring onions, and sliced spring onion greens to a bowl.
Add some lemon zest, generous splash of fresh lemon juice, a solid glug or two of olive oil, and spring onion salt and pepper. Mix together and then taste. Continue to adjust the seasoning (usually more salt and lemon, but you may want to add more olives or dates).
Plate and top with an extra drizzle of olive oil (I love the Meyer lemon oil from @likefamily___ ) and a sprinkle of spring onion salt.
