In a large pan add the oil and cook the onion until softened.
Stir in the zucchini and peppers and cook for 2 minutes.
Add the garlic, pumpkin, lentils, tomatoes, stock, herbs and salt and pepper to taste. Stir until well combined and bring to the boil.
Reduce heat and simmer for 10-15 minutes.
Mix the ricotta and sour cream together with half the cheese. Season well.
Place 1/3 of the lentil sauce in the base of an ovenproof dish then top with lasagne sheets next layer 1/3 lentil sauce and 1/3 ricotta mixture, repeat. Top last layer with ricotta mixture and sprinkle with grated cheese. Depending on the shape of your dish you may need to adjust the layering.