Prepare the béchamel: Melt butter in a saucepan, add flour and mix well. Pour in hot milk in small increments, stirring constantly to avoid lumps, and bring to a boil. Season with salt, a pinch of nutmeg and set aside.
Pre-heat oven to 350 °F and grease a baking dish with butter.
In a saucepan, slowly brown the onions, celery and carrots with olive oil and a bunch of rosemary. Add chicken and let it brown as well.
Add tomato paste, cover with water, and let it cook for 10 minutes.
Season with salt and pepper. Remove the rosemary and set aside.
In the greased baking dish pour a first layer of veggie chicken sauce and béchamel sauce on the bottom then add dollops of pesto.
Next add a layer of Lasagne sheets, followed by another layer of sauces.
Sprinkle with cheese and continue to build the Lasagne, alternating the pasta and sauces. Make sure the final layer is sauce, and sprinkle with remaining cheese.
Bake for 20 minutes at 350 °F or until the cheese is crispy and golden brown.
Remove from the oven when it is perfectly baked, crispy, and golden brown.
Let it cool for about 10 minutes before serving. This allows the Lasagna to hold its shape when serving.
