Preheat your oven to 375°F (190°C).

Spinach Cream Sauce: Heat olive oil in a large skillet over medium heat. Add the chopped onion and sauté until translucent.

Add butter to the skillet and let it melt. Stir in the flour and cook for about 2 minutes to form a roux.

Gradually whisk in the chicken broth and half and half (or heavy cream and milk). Cook, stirring constantly, until the sauce thickens and comes to a simmer.

Add the chopped spinach, minced garlic, salt, and black pepper to the sauce. Cook for another 2-3 minutes until the spinach wilts and the sauce is well combined. Remove from heat and set aside.

Cheese Sauce: In a separate bowl, combine ricotta cheese, egg, chopped parsley, and grated Parmesan cheese. Mix until smooth and well combined.

Assembling the Lasagna: Spread a thin layer of the spinach cream sauce on the bottom of a 9x13-inch baking dish.

Layer lasagna noodles over the sauce, followed by a layer of the ricotta cheese mixture, mozzarella cheese, and more spinach cream sauce. Repeat layers until all ingredients are used, ending with a final layer of sauce and mozzarella cheese on top.

Baking: Cover the baking dish with aluminum foil and bake in the preheated oven for 30 minutes.

Remove the foil and continue baking for an additional 15 minutes or until the cheese is bubbly and golden brown.

Let the chicken lasagna cool for a few minutes before slicing and serving.