Preheat the oven to 200°C, fan 180°C, gas 6.
Put the veg, tomato sauce and some seasoning in a pan and bring to the boil. Simmer for 5 mins, stirring occasionally, or until the vegetables are tender.
Meanwhile, soak the lasagne sheets in a bowl of boiling water for 5 mins and cook the spinach according to the packet instructions. Drain the spinach and season. Put in a bowl, stir in the butter, half the cheese and half the crème fraîche.
Spoon a third of the veg in tomato sauce into the base of a 1.7 litre baking dish and top with a lasagne sheet. Spoon over half the spinach mixture and top with a further third of the tomato sauce. Cover with a lasagne sheet, tucking in any stray edges and top with the remaining spinach mixture. Spoon over the rest of the tomato sauce and a final lasagne sheet. Finish with the remaining crème fraîche and the rest of the cheese.
Bake for 20-25 mins or until brown and bubbling. Serve with a salad.