First, prepare all the veggies. Coarsely grate the courgette then transfer to a colander and use the back of a spoon to squeeze out the excess liquid. Trim the green part of the leek and wash well before slicing into 0.5cm slices. Finely dice the onion, garlic and celery.

Place a large casserole pan onto a medium heat and add the olive oil. Once hot, add the onion, celery, garlic and leek, along with a large pinch of salt and pepper and allow them to slowly cook for 10-15 minutes. Ideally they should be just translucent but without colour. Remove from the pan and set to one side.

Meanwhile, preheat the oven to 200°C/180°C fan. Make the bechamel sauce by first melting the butter in a small, solid-based pan. Once melted, add the flour, stir well and cook until the mixture becomes grainy and slightly golden. Now pour in a 1/3rd of the milk. Stir to combine and bring to a simmer before adding the next 1/3rd. Do this until the sauce is smooth and the milk is all gone. You may want to use a whisk to get a super smooth sauce. Add the ground nutmeg the Dijon mustard and half of the grated parmesan cheese. Combine well, season with salt and pepper and leave to one side.

In the same pan that you cooked the onions in, add the grated courgette and spinach. Turn the heat to high and cook for 3-5 minutes, until the spinach has wilted and the courgettes have steamed. Tip the contents of the pan into a colander set over a large bowl and use a wooden spoon to remove the excess liquid. Return the spinach and courgettes to the pan, along with the cooked onion, leeks and celery. Stir through the pesto and have a taste to check it's all seasoned well. You could add a small pinch of nutmeg here if you like.

Spoon half of the green veggie mixture into a 20x30cm ovenproof dish (to serve 4) and even it out, making sure it goes right into the corners. Tear over half of the mozzarella and top with half of the fresh lasagne. Spoon over half of the béchamel and then repeat the layers with the remaining ingredients, finishing with a layer of béchamel. You may find you may only have space for 2 sheets per layer, it will depend on the size and shape of your baking dish. Sprinkle the grated veggie hard cheese all over the béchamel.

Place the whole dish into the oven and bake for 30-40 minutes, until golden and bubbling on top. Leave the lasagne to stand for 10 minutes, before serving with a green salad dressed with a little balsamic vinegar and olive oil, if you wish.