Chop the tomato finely and stew it with the sauce gently. Add the minced meat and stir well, season with salt and pepper to taste and allow to thicken. In a separate bowl, prepare the béchamel sauce - put the oil in to heat up and fry it until the flour is browned, add the milk.
Prepare the lasagna sheets according to package directions. Arrange them in an oven dish, starting with a layer of sheets, then a layer of the tomato sauce with minced meat, then put béchamel sauce on it and repeat until out of ingredients. Be sure to finish off with lasagna sheets, covered only with béchamel sauce.
Sprinkle with plenty of grated cheese and bake in a moderate oven for 30-40 minutes.