1. In a non-stick pan, fry the onions in the olive oil until they soften, then add the courgette, peppers and mushrooms. Fry for around 10 minutes, stirring frequently.
2. Add the garlic, red lentils, tinned tomatoes, oregano, sugar and then crumble in the vegetable stock.
3. Fill one tomato tin with water and pour into the pan. Allow all of the ingredients to simmer for another 15 minutes, stirring frequently.
4. Add the spinach leaves and allow to wilt for 1-2 minutes.
5. To prepare the lasagne cream: heat some olive oil in a saucepan and add the flour, stirring constantly. After 1 minute, add the milk, nutritional yeast, nutmeg, salt and pepper and whisk non-stop for 3-4 minutes, until the cream thickens.
6. Add a layer of vegetables to a non-stick pan (covering around 1/3 of it), then add a layer of lasagne sheets, and repeat for a second layer.
7. Add half of the cream to the second layer of lasagne sheets, add another layer of vegetables and sheets on top, then pour over the rest of the cream.
8. Cook the lasagne in a pre-heated oven (190 degrees), until the top layer of cream is golden brown. Leave the lasagne to cool for 5 minutes, before serving.