Preheat your oven to 375°F (190°C). Gather your ingredients and prepare your workspace.

In a large skillet, heat 2 tablespoons of olive oil over medium heat. Add 3 cloves of minced garlic and 1 tablespoon of chopped fresh rosemary, sauté for about 2-3 minutes until fragrant.

Add 4 tablespoons of unsalted butter to the skillet and let it melt. Whisk in 1/4 cup of all-purpose flour, cooking for 1 minute until a roux forms. Gradually stir in 2 cups of whole milk and continue whisking for about 5 minutes until the sauce thickens.

Once thick, add a pinch of nutmeg and 1/2 cup of grated Parmesan cheese, stirring until melted. Fold in 2 cups of shredded chicken and optionally, handfuls of baby spinach.

In a 9x13 baking dish, spread a thin layer of the béchamel, layer 3 no-boil lasagna noodles, then one-third of the chicken béchamel mix and a handful of mozzarella. Repeat the layers two more times.

Cover with aluminum foil and bake in the preheated oven for 30 minutes. Remove foil and bake for another 10-15 minutes until bubbly and golden.

Let the lasagna rest for about 10 minutes before slicing and serving.