Peel and slice the courgettes, carrots and onions, not too thick.
Slice the potatoes and peppers.
In a large deep sided frying pan place a tbsp of oil. Then add the onions and garlic. Fry until soft.
Then add the carrots, peppers, courgettes, potatoes, salt, pepper and rosemary. Fry for 2 mins, then add the marinara sauce. Cover and allow to simmer for 15 minutes. Add some tomato puree to thicken sauce if needed.
In a large oven dish layer the base with some lasagne sheets, then pour in 1.3 of the mix from the frying pan, followed by a third of the white sauce. Repeat this twice more to fill the dish.
Bake in the centre of the oven for 35 minutes. Remove from oven and cover the top with grated cheese.
Return to the oven for another 10-15 minutes until the cheese has melted and turned golden brown.