Put the garlic, basil, pine nuts, lemon juice, olive oil, Parmesan cheese, salt and pepper into a food processor. Whiz it all up and then stir, add a bit more olive oil if needed and whiz up again. Keep doing this until you have a smooth sauce.
For the bechamel sauce:
In a saucepan, melt the butter. Whisk in the flour and stir for a couple of minutes, until the flour is golden brown. Add about a third of the milk, slowly, and whisk over medium heat. Add the pepper. When the sauce is smooth, add another third of the milk and whisk. When the sauce is smooth again, add the rest of the milk and whisk until smooth.
Smear a little of the bechamel sauce to coat the bottom of a lasagne dish. Lay first layer of lasagne sheets. Add enough bechamel to coat the sheets. Add some pesto and spread into the bechamel. Add a handful of the 130g grated Parmesan cheese. Continue to layer the lasagne sheets, bechamel, pesto and Parmesan cheese until the last layer of sheets. On top of this, just spread the bechamel only, add the rest of the Parmesan cheese and top with the mozzarella cheese. Sprinkle the oregano on top. Wrap tightly with foil.
Bake for 1 hour (if using regular, cooked lasagne sheets) or 1 hour and 15 minutes (if using no-boil sheets). Remove foil and bake for 10 minutes more, until top is golden. Remove from oven and allow to sit for 15 minutes before slicing.
Parmesan cheese is not truly vegetarian, as it contains animal rennet. To make this dish 100% vegetarian, omit the cheese or find a suitable vegetarian substitute made without animal rennet. In supermarkets look for the 'parmesan style hard cheeses' which are suitable for vegetarians.