Prepare the aubergine by cutting off the stalks, and cut lengthwise into approximately 1cm thick slices. (The aubergines, that is, not the stalks!)
Mix the lentils and walnuts into the tomato sauce, and then place 2-3 ladlefuls on the bottom of a lasagne dish.
Heat your grill, and brush with a little oil. Arrange the aubergine slices on the grill plate, and brush each one with a little more oil. Close the top, and cook for a few minutes, until the slices are lightly-browned, and softened enough to work with. Unless you have a large grill, you'll probably need to do this in two batches.
Carefully remove the aubergines slices from the grill, and place onto a large chopping board or clean work surface.
Spread each slice with some of the ricotta, then a tablespoon of the tomato sauce mixture. Add some chopped spinach, some torn basil, and a few grinds of black pepper.
Roll up each slice, and place into the oven dish.
Loosely cover with tin foil, and bake in a hot oven for 40-45 minutes, until the aubergines are cooked through.
Warm the tomato sauce through while the aubergines are cooking.
Once cooked, remove from the oven, take off the foil, spoon over some more tomato sauce, and finish with the vegan parmesan and a few grinds of black pepper.
Serve immediately. (It doesn't really keep well, and it can't be frozen.)