Preheat oven to 375 degrees.
Cut spaghetti squash in half length-wise. Scoop out seeds. Rub flesh with olive oil and place flesh side down on a shallow baking sheet. Bake for 40-50 minutes until a fork pierces the skin easily and the flesh can be easily pulled into strands with a fork. Allow to cool slightly, then using a fork scrape squash into a bowl. Season with butter, salt & pepper.
In a small bowl combine ricotta cheese, parmesan cheese, egg and garlic & herb seasoning.
In a small bowl combine cooked chicken cubes with pesto sauce.
In a 2 quart casserole or baking dish, layer ingredients lasagna style. Cover bottom of pan with 1/2 cup marinara sauce. Top with 1/4 of the spaghetti squash. Top that with half of the ricotta mixture and a sprinkle of mozzarella. Top with 1/2 cup marinara sauce, 1/4 spaghetti squash, 1/2 pesto chicken, sprinkle of mozzarella cheese. Repeat with marinara, squash, ricotta, mozzarella, marinara, squash, pesto chicken, mozzarella.
Bake at 375 for 25-30 minutes. Allow to sit for 10 minutes before serving to allow the juices to soak up.