Melt the butter in a large skillet over medium-high heat.
Add the spinach in batches, cooking each just until wilted, then season lightly with salt and pepper.
Transfer wilted spinach to a bowl, let cool slightly, then squeeze out excess moisture and coarsely chop.
In a mixing bowl combine the chopped spinach with chopped basil, minced garlic, ricotta, eggs, grated Parmesan, 1 cup shredded mozzarella, Italian seasoning, 1/2 teaspoon salt, and 1/4 teaspoon pepper; mix until evenly combined.
Cook the lasagna noodles according to package directions until al dente; drain and set aside.
Preheat the oven to 375°F (190°C) and coat a 9x13-inch baking dish with cooking spray.
Spread a thin layer of marinara sauce over the bottom of the prepared dish.
Place a layer of noodles over the sauce, spread one-third of the spinach-ricotta mixture over the noodles, then spoon one-third of the marinara sauce on top.
Repeat the noodle, cheese mixture, and sauce layers two more times, ending with sauce on top.
Cover the lasagna with foil and bake for 40–45 minutes.
Remove the foil, sprinkle the remaining 2 cups shredded mozzarella over the top, and bake uncovered for an additional 15 minutes or until cheese is melted and bubbly.
Garnish with chopped parsley and chopped basil, let the lasagna rest 10–15 minutes, then cut into 9 slices and serve.