Lentil lasagne

Name: Lentil lasagne
Ingredients: 1 tbsp olive oil; 1 onion, chopped; 1 carrot, chopped; 1 celery stick, chopped; 1 garlic clove, crushed; 2 x 400g cans lentils, drained, rinsed; 1 tbsp cornflour; 400g can chopped tomatoes; 1 tsp mushroom ketchup; 1 tsp chopped oregano (or 1 tsp dried); 1 tsp vegetable stock powder; 2 cauliflower heads, broken into florets; 2 tbsp unsweetened soya milk; pinch of freshly grated nutmeg; 1 tbsp dijon mustard; 2 tbsp nutritional yeast; 9 dried egg-free lasagne sheets