For the tomato sauce, chop the onions, garlic and simmer in olive oil with the cumin, chilli flakes and sugar. Allow to brown lightly than add the lemon and tomato pulp and simmer until well thickened. Next prepare the chicken filling by chopping the garlic and sauté with the chicken, curry, celery and spice until cooked through. Add in the chopped leeks and stir well. Allow excess water to absorb and remove from heat. To make the sour cream, squeeze the lemon juice in the chilled fresh cream and stir, keep in the fridge until you are ready to serve. To put the dish together, Using a baking tray start by spreading some tomato sauce as a base in the bottom of an oven proof dish, then lay the lasagna sheets. Add sauce tomato sauce in each layer with the chicken filling. Finish the top with cherry tomatoes and grated cheddar and bake. Once baked sprinkle with chives and serve with sour cream.