Prepare the meat sauce by heating the oil in a pan.
Once the oil is hot, saute the onion until it turns soft.
Add the ground beef and cook until it browns.
Pour-in the diced tomatoes. Let boil and simmer for 10 minutes.
Add the tomato paste. Stir and cook until the sauce thickens.
Add salt and pepper to taste. set the meat sauce aside.
Meanwhile, prepare the mornay sauce by melting the butter in a saucepan.
Once the butter melts, gradually add the flour. Stir and cook in low to medium heat until the flour absorbs the butter (around 2 minutes).
Pour the milk in the sauce pan. Stir to dilute the flour and butter.
Add Parmesan cheese. Stir and cook until the sauce thickens. Set aside.
Preheat oven to 350F.
At this point, we have the meat sauce and mornay sauce ready. Assemble the lasagne by arranging the lasagne pieces in a baking pan. Line the oven-ready lasagne at the bottom of the pan. Top the first layer with 1/3 of the meat sauce. Top the meat sauce with spinach. Pour a quarter (1/4) of the mornay sauce over the spinach and spread until the entire pan is covered. Do this step 2 times more so that you will have 3 layers in the pan.
Top the last layer with lasagne pieces then pour and spread the remaining mornay sauce on top. Sprinkle sharp cheddar cheese on top.
Place in the oven and bake for 40 minutes.
Remove from the oven. Serve.
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