Finely chop the onions. Prepare garlic and cut very finely, then prepare any other vegetables. Place on different tray until needed and open the cans of chopped tomatoes.
Add olive oil to a large saucepan and fry the mince until brown, add garlic after 3 minutes of adding the mince. Add the onion and any other vegetables then cook for a further 5 minutes. Stir frequently to make sure the mixture does not stick!
Add the cans of chopped tomatoes and stir well with a wooden spoon and then add the tomato puree. Cook with a lid on for 10 minutes on a low heat, checking every 2 minutes. Season with salt and pepper to taste.
Preheat oven to 190 C / Gas 5.
Combine margarine, flour and milk in a separate sauce pan. Cook stirring continuously until the sauce thickens. Add 50g of the cheese. Heat through, but do not allow to get too thick. Season to taste.
Lightly grease the bottom of an oven proof casserole dish. Pour one third of the cheese sauce on the base and then top with lasagne sheets. Spread half the meat sauce over and then add another third of the cheese sauce over, top with more lasagne sheets.
Spread the rest of the meat sauce over and add more lasagne sheets then cover with rest of the cheese sauce. Cover with rest of the cheese.
Cook for 20 mins in the preheated oven until cheese is melted and golden brown on top.