To make meat sauce: Chop onions, peppers, mushrooms and garlic. Put mince into a large pan and fry until completely brown, stirring all the time with a wooden spoon. Add onions and garlic to mince and cook for 3-4 minutes. Add chopped peppers, chopped mushrooms, tin of tomatoes and tomato sauce to the mince mixture. Bring to the boil and leave to simmer on a low heat for 15-20 minutes.
To make the cheese sauce: Melt the margarine in a saucepan. Add the flour and cook over a low heat for 1 minute, stirring all the time. Remove from the heat and cool slightly. Add the milk, salt and pepper stirring all the time.
Return to the heat and bring to the boil. Keep stirring. Add cheese. Reduce heat and cook slowly for 5 minutes.
Put layer of meat sauce in the bottom of casserole dish, cover with easi-cook lasagne sheets. Make 1 or 2 more layers as above finishing with a layer of lasagne sheets. Cover with cheese sauce. Sprinkle with remainder of cheese and bake for 30 to 40 minutes.