Start by making the filling mixture. In a large pan heat up the oil, add the garlic, onion and celery and cook gently for about 3 minutes until softened.Add the lentils, carrot, zucchini and kale, stir and cook for a minute.Stir in the chopped tomatoes, tomato puree, oregano, paprika, salt and pepper and water. Cover, bring to the boil and let the mixture simmer away for 20 minutes. Don’t forget to stir it occasionally to prevent it sticking to the bottom of the pan.Remove from the heat, stir inthe parmesan cheese and adjust the seasoning if needed.
Preheat the oven to 375 F/ 190 C/ gas mark 5. Grease the bottom of a lasagne dish (approx. 20 cm x 30 cm) with a little oil. Set aside.
To make the white sauce in a saucepan melt the butter over a medium heat, add the flour and whisk quickly until smooth. Pour in some of the milk, increase the heat and whisk until the sauce thickens then add the rest of the milk and whisk until the sauce starts bubbling up. Remove from the heat, season lightly and set aside for 5 minutes.
Assemble the lasagne. Lightly grease the bottom of your lasagne dish and cover with 3 lasagne sheets.Cover with half of the filling mixture and drizzle half of the bechamel sauce over the top.Cover with 3 more lasagne sheets and add the rest of the filling mixture then place the final 3 lasagne sheets on top. Pour the rest of the bechamel over the top ensuring it covers the pasta sheets completely and scatter the cheddar over the whole thing.
Bake the lasagna in the lower part of the oven for 40 minutes. If the lasagna starts browning too much cover loosely after 30-35 minutes.Remove from the oven, set aside for 10 minutes then serve.
Cheese: I used a moderate amount but you can adjust the amount according to your preference.
Bechamel sauce: The sauce should be quite thick and cover the top lasagna sheets evenly.
Lentil sauce: Taste the sauce before assembling the lasagne to ensure it is well seasoned.
If you can't find Puy lentils you can use ordinary green lentils or beluga (black) lentils.
Use grated mozzarella for the top instead of the cheddar if preferred.
I only used oregano and paprika but you can also add basil into the lasagna filling.
If you prefer not to use parmesan cheese use vegetable stock instead of water and do not season the filling mixture until it's cooked so you can taste it and decide if it needs more salt (add plenty of pepper though).
It is important to bake your lasagna in the lower part of the oven so it doesn't brown too quickly.
Best served hot. Leftovers can be refrigerated for up to 3 days. Reheat in a microwave.