Mince the garlic and chop the onion. Shred the rotisserie chicken into bite-sized pieces and measure your cheeses. Rinse and roughly chop the spinach if the leaves are large. Have your cooked lasagna noodles ready; if using dried noodles, cook them according to package instructions until al dente and drain on a lightly oiled tray so they don’t stick.

Heat a large skillet over medium-high heat. Add the butter and let it melt, swirling the pan to coat the bottom. Add the minced garlic and chopped onion. Sauté, stirring occasionally, until the onion becomes translucent and fragrant — about 4–5 minutes.

Add the fresh spinach to the skillet and stir until it wilts. This happens quickly.

Reduce the heat to medium-low. Pour in the heavy cream, stirring to combine with the onion and spinach. Add the grated Parmesan and ricotta cheese, stirring until the cheeses melt into a smooth sauce. Adjust seasonings with black pepper and salt.

Stir in the shredded rotisserie chicken until evenly coated. Let the sauce come to a slight simmer, then remove from heat.

Preheat your oven to 350°F (175°C). Grab a 9 x 13 inch deep baking dish and spoon a large spoonful of the chicken Alfredo mixture into the bottom to lightly coat the pan.

Lay out your cooked lasagna noodles over the coated bottom. Spoon a generous amount of the chicken Alfredo mixture over the noodles and sprinkle about one-third of the shredded mozzarella.

Continue layering with noodles, chicken Alfredo, and mozzarella until all ingredients are used. The final layer should be the chicken Alfredo mixture topped with the remaining mozzarella.

Cover the lasagna tightly with aluminum foil and bake in the preheated oven for 35–40 minutes.

Remove the foil and switch to broil. Broil for 2–3 minutes until the mozzarella is golden and bubbly.

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