Preheat the oven to 200ºC/400ºF/gas 6. Use a speed-peeler to strip the lemon zest into a large casserole pan on a medium heat, then add 2 tablespoons of oil and the garlic bulb. Peel and quarter the onions and separate into petals, destone the olives, and slice the potatoes 1cm-thick. Add to the pan, pick in the oregano leaves and cook for 5 minutes, or until just starting to soften and colour. Quarter and add the tomatoes, then season to taste with sea salt and black pepper.
Pour 500ml of water into the pan and bring to the boil, stirring well and scraping up any sticky bits from the bottom. Discard just the tatty outer leaves from the cauliflower, then cut a cross into the stalk and push it right down to the bottom of the pan. Drizzle with 1 tablespoon of oil, cover, then place in the oven for 1 hour, or until golden and caramelised, basting occasionally and removing the lid halfway through. Remove the cauliflower to a serving platter and pick out the garlic bulb, then place the pan back over a medium heat on the hob, stir in the peas or broad beans, and simmer for 5 minutes. Carefully squeeze all the garlic out of the skins and stir back into the pan. Taste and tweak the seasoning, if needed, then pour over the cauliflower and finish with a good squeeze of lemon juice.
I love to serve this with bread to mop up the juices – heavenly!
When adding the peas or broad beans, this is your opportunity to add extra quick-cooking greens like chard, spinach, asparagus, tenderstem broccoli – this will lift the dish and really reflect the seasons.