Cut the cauliflower into medium, similar-sized florets. Wash them and let them drain.
In a deep saucepan or large pot (preferably with lid), heat the olive oil over medium to high heat. Add the onion for 2-3 minutes until richly browned. Add carrots, celery, parsley, cauliflower leaves, the bay leaf, the cinnamon stick and tomatoes (or passata or canned tomato) for another 5 minutes.
Add the florets. Take the heads and soak them in the sauce for 5 seconds, just to take some nice color. Place stalks to the bottom of the pan/pot and the heads up.
Add the water (or vegetable stock) with the dissolved tomato paste. Bring to a boil and then immediately reduce the heat to low. Close the pot/pan lid and simmer for 15 mins or until cauliflower stalks become tender (pierce them with a fork to see if they are soft enough). Add more water if the mixture is dry and needs a few more minutes.
Add salt and pepper. Use two folks to turn carefully the florets upside down and simmer for another 5 minutes. Last check if florets are tender enough for your taste.
Remove from the heat and stir through the lemon juice. Discard the bay leaf and the cinnamon stick. Drizzle some more olive oil and serve with feta cheese and homemade bread.