In a large bowl, add the tomato sauce, a pinch of salt, black pepper, thyme, oregano, Greek yogurt, and mix.
In a large pot, sauté the onion in olive oil over medium-high heat.
Add the garlic, and mushrooms, and sauté 2 minutes more.
Add the spinach and salt and cook for 5-10 minutes until the spinach has thawed and all its liquids have been released. It should be juicy so that the lasagna can use its moisture to soften and taste better.
When it is ready remove the pot from the heat.Preheat the oven to 200 ° C.Brush some olive oil and 3 tablespoons of the tomato sauce to coat the bottom of the baking dish or your pyrex.
Add the first layer of lasagna.
Now, add 1/3 of the spinach mixture.
Top with 1/4 of the tomato sauce and 1/4 of cheeses.
Make two more layers of all the ingredients lasagna, spinach, tomato sauce, and cheese.
In the end, finish with the last layer of lasagna and the rest of the tomato sauce and cheese.
Bake for 30 minutes until you see delicious bubbles on the side of your baking dish and it has a nice crispy crust.