Preheat your oven to 375°F and grease a large baking dish.
In a skillet, heat olive oil on medium and sauté garlic, onion, and mushrooms until soft.
Add shredded chicken to the skillet and pour in the chicken stock.
Let it simmer until the mixture is well combined and stock is mostly absorbed.
For the béchamel, melt butter in a saucepan over medium heat, stir in flour, then gradually add milk, whisking continuously until thick.
Season with salt and pepper.
In your baking dish, spread a layer of the chicken mixture, top with béchamel, and then layer with lasagna sheets.
Repeat the layering process until ingredients are used.
Top with béchamel and sprinkle with Parmesan cheese.
Bake for about 30-35 minutes until golden and bubbling.
Allow the lasagna to cool slightly before serving.