Heat the oil in a pot on medium-high heat.
Add onions (chopped or blended) to the pot. Sauté for about 5 minutes. Add minced garlic to the onions and sauté them together for about 20 minutes. If the onions start to stick to the bottom of the pan, add a little bit of water to deglaze.
Once the onions are a deep golden-brown colour, add the minced turkey. Break up any large meat clumps with your spatula. Cook the meat for about 10 minutes.
Add the tomato sauce. Turn the heat down to medium-low and let it simmer for a good 20 minutes. Stir every few minutes to make sure it's not sticking to the bottom of the pot. Add spinach and let it simmer for another 5 minutes.
Cook the sauce until it gets to your desired thickness.. the longer you cook it, the thicker it becomes. Add in spinach and cook for 2 more minutes. 6. Season with salt, pepper and oregano (about 1/4 teaspoon each).
Make white sauce: in a separate pot, melt margarine over low heat. Add 2 tbsp of flour. Stir until mixture is golden brown, then quickly add milk. Constantly stir until mixture thickens.
Cook lasagna sheets and make three layers.