1.Preheat oven to 200°C. Lightly grease a 1-litre (4-cup) ovenproof dish.
2.Heat half the oil in a medium frying pan over high heat; cook mushrooms, stirring, for 5 minutes or until browned. Remove from pan.
3.Heat remaining oil in same pan over medium heat; cook onion and garlic, stirring, for 3 minutes or until onion is softened.
4.Increase heat to high, add mince to pan; cook, stirring, for 3 minutes or until browned. Return mushrooms to pan with tomatoes and oregano; simmer, covered, over low heat, for 10 minutes, stirring occasionally.
5.Meanwhile, combine milk and cornflour in a small saucepan; whisk until smooth. Cook, stirring, over medium heat, for 5 minutes or until mixture boils and thickens. Remove from heat.
6.Squeeze excess moisture from spinach.
7.Spoon a third of the mince mixture into prepared dish. Cover with one lasagne sheet. Spoon over another third of the mince mixture; top with spinach and another lasagne sheet. Spoon over remaining mince mixture; cover with lasagne sheet. Spoon over white sauce; sprinkle with cheese.
8.Place dish on an oven tray; bake for 45 minutes or until lasagne is tender and cheese is golden. Sprinkle with extra oregano leaves, if you like.
You could make this lasagne with wholemeal pasta sheets for extra fibre. This lasagne will freeze well so make a double or triple batch in a larger ovenproof dish and freeze (once cooled) in individual airtight containers for up to 1 month. You could replace the oregano with basil. Add a little freshly grated nutmeg to the white sauce, if you like. We used cup mushrooms here, but use your favourite type. Some butcher’s sell a pork and veal mixture, which is what we’ve used here. If it is not available, buy half the amount in pork mince and half the amount in veal mince.