Pre-heat the oven to 220°C / 200°C fan / gas 7 and line 2-3 large baking trays with parchment paper and brush with olive oil.
Trim the ends off the courgettes then cut them into long slices, about 5mm each. (You need at least 18 long slices in total).
Arrange the slices on the prepared baking trays and brush the tops with olive oil. Season lightly with salt then bake until tender and starting to go golden at the edges, 10-12 minutes. Set aside to cool.
Turn the oven down to 200°C / 180°C fan / gas 6.
Heat a drizzle of olive oil in a large frying pan over medium high heat. Once hot, add the leeks and fry until tender and just starting to go golden, about 7-8 minutes, stirring regularly. Remove from heat then stir in the lemon zest, half of the basil and about 45g of the pine nuts.
Cut each lasagne sheet lengthways into three long strips, each about 5cm wide. Place in a large bowl and then pour in enough cold water to submerge the strips. Leave to soak for about 5 minutes.
In a small bowl mix the remaining basil with 3/4 of the tomato sauce. Spread this over the base and up the sides of a baking dish, about 25 x 15cm (A smaller sized dish is better than one that’s too big as you want the rolls to sit snugly).
Remove 6 pasta strips from the water and shake off excess water. Arrange them on a chopping board or clean surface. Spread a teaspoon of the remaining tomato sauce over each strip, then lay a courgette slice on top. Tip: If you have more than 18 courgette slices the extras can be torn into smaller pieces and used to cover the pasta strips from end to end.
Take a third of the cooked leek mixture and divide evenly between the 6 strips, scattering the leek over the courgette.
Tear off 6 pieces of mozzarella and place each piece at the end of each strip. Roll up tightly from the mozzarella end then arrange them in the baking dish standing up so you can see the spiral, and nestling them together snugly. Repeat twice more in batches of 6 until all of the pasta and filling ingredients have been used.
Brush the tops of the rolls with olive oil then cover the dish tightly foil.
Bake until the pasta is tender in the middle and crisp at the edges, 35-40 minutes.
Remove the foil then sprinkle over the reserved basil, Dubliner Three Cheese Blend and pine nuts. Return to the oven until the cheese is melted and bubbling.