Heat the oven to 200C / 180C Fan / Gas mark 6.
Heat the oil in a large saucepan.
Add the onion and garlic and cook until softened.
Add the bacon and mushrooms and continue to cook for 1-2 minutes.
Add the chopped tomatoes, parsley & puree, bring to the boil and simmer for 5 minutes.
Stir in the flaked tuna and season to taste. Mix well.
Place 1/2 of the tuna mixture in a large ovenproof dish.
Cover with 3 sheets of lasagne.
Repeat the layers, finishing with a layer of lasagne.
Pour over the white sauce, then sprinkle with the grated cheese.
Bake in the preheated oven for 45 minutes.
Serve with a fresh green salad or garlic bread
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