In a large skillet, cook the ground beef until it has browned and drain off the fat. Stir in the pasta sauce. Set aside.
In a medium bowl, add in the ricotta cheese, Parmesan cheese, egg, Italian seasoning, and stir until combined. Add in salt and pepper to taste. Set aside.
Preheat the oven to 350 degrees F.
In a square baking dish, spoon enough meat sauce on the bottom to cover the bottom of the dish. Top this layer with enough oven-ready lasagna noodles to cover. Cover the noodles with enough additional meat sauce to cover, top with half of the baby spinach, and spread half of the ricotta mixture evenly over the top.
Sprinkle with half of the shredded mozzarella cheese. Top with the noodles, meat sauce, spinach, ricotta mixture, and the rest of the mozzarella cheese.
Cover the baking dish with aluminum foil and place into the oven to bake for 20 to 25 minutes, until the cheese is bubbling and melted. Remove the foil and continue to bake for an additional 5 to 10 minutes, until the top has lightly browned.
Allow the lasagna to cool for a few minutes prior to serving.