To make the harissa mayo, peel and bash the garlic in a pestle and mortar with a little sea salt, then muddle in the mayo. Add 2 teaspoons of harissa, followed by the zest and juice from ½ a lemon, then mix well, taste and add a little more lemon juice, if needed. Transfer to a bowl, drizzle over the rosewater and ripple through the remaining harissa. Set aside.
Scrunch the oregano flowers into a liquidiser and discard the stalks, then add the fennel and a teaspoon each of salt and white pepper. Blitz to a fine powder, then place into a large bowl with the flour and stir to combine.
Wash and pat dry the squid, then slice and open out the tubes like a book. Cut a criss-cross pattern onto the surface, then add to the flour along with the tentacles and toss well to coat.
Place a large, deep saucepan over a medium-high heat. Fill three-quarters full with vegetable oil and allow to heat up. To test if the oil is hot enough, drop a piece of bread into the pan – if the bread floats to the surface, sizzles and turns golden, it's about right. Shake off any excess flour from the squid, then use a slotted spoon to carefully lower into the hot oil (you’ll need to do this in batches). Cook for 3 to 4 minutes, or until golden, crisp and cooked through. Transfer to a double layer of kitchen paper to drain, then repeat with the remaining squid.
Rinse the parsley sprigs under cold running water, shake off any excess water, then pick the leaves into the flour. Toss to coat, then lower into the hot oil for a few seconds, or until crisp. Transfer to kitchen paper, then slice 1 lemon horizontally into thin discs, dip into the flour and place in the hot oil for around 1 minute, or until crisp.
Scatter the crispy parsley and lemon slices over the squid, then serve with extra lemon wedges for squeezing over and harissa mayo for dunking.