Preheat oven to 375℉. Lightly spray a 8x8 baking dish.
Start the water for the lasagna noodles. Once the water is boiling, cook the noodles for about 10 minutes until al dente. (Check the package instructions.)
Meanwhile, in a medium bowl, combine chicken, ricotta cheese, feta cheese, parmesan cheese, milk, and pepper to create the filling.
Wilt spinach either in the microwave for 30-60 seconds, or in a sauté pan with a bit of oil. Use a paper towel to remove excess moisture. Chop wilted spinach roughly and mix with the filling.
Chop mushrooms and onion and sauté in olive oil until soft and the mushrooms have released their juices. Add the marinara sauce and stir.
Spread about a ½ cup of the filling on each lasagna noodle. I like to add filling to all the noodles before rolling to assure an even amount on each noodle.
In an 8 x 8-inch baking dish, spread ½ cup marinara sauce. Starting on one end, roll each noodle and place seam-side down in sauce in the baking dish. Top with remaining marinara sauce, mozzarella cheese and additional parmesan cheese.
Cover the pan with foil. Bake for 30 minutes, or until hot and cheese is melted. Allow to rest for 5 minutes before serving.