Preheat the oven to 350° F. Coat a 9 x 13 -inch casserole dish with cooking spray.
Cook manicotti in salted water according to package directions. Avoid stirring to make sure that the pasta stays whole. Drain.
While the pasta cooks, combine the ricotta, chicken, spinach, 1 cup of mozzarella, parmesan, salt, and pepper in a large bowl.
Spread ½ cup of the sauce on the bottom of the prepared casserole dish.
Fill each manicotti with the ricotta mixture and arrange in the dish in a single layer.
Top with the remaining 1 ½ cups marinara and remaining mozzarella.
Bake for 30 to 35 minutes, until melted and bubbly.
Let cool for 10 minutes. Sprinkle with fresh herbs to garnish, and serve warm.
