In a pot, add olive oil and fry the chicken until it gets color on each side.
Add the seasoning.
Remove from the pot, turn off the heat, and let the chicken cool down a bit.

In the same pot, over low heat, add chopped onion, sliced mushrooms, and diced tomatoes. Let it simmer for a bit.
Cut the chicken into cubes and add it back into the pot.
Let the sauce cook over low heat. Add cheese and pepper.

In another pot, bring water to a boil and add a little salt. Once it boils, add the lasagna sheets one by one. When they are ready, transfer them to a bowl of cold water to cool down. After cooling, drain them. Transfer to a bowl and drizzle with a bit of olive oil.

In a small saucepan, melt the butter and then add the flour. Stir well, then gradually add the milk, a bit of salt, and nutmeg while mixing. Lower the heat.

In a baking dish, brush a bit of oil to coat the bottom.
Start with a layer of pasta, then a layer of the filling, another layer of lasagna, and then the remaining filling.
Add another layer of lasagna on top and cover it with the béchamel sauce.
Sprinkle with cheese and bake in the oven at 200ºC (390ºF) for 15-20 minutes.

Let it cool for a bit before serving.