Preheat oven to 375°F (190°C).
In a saucepan, heat olive oil over medium heat. Add chopped onion and garlic, cook until soft.
Add spinach, oregano, basil, salt, and pepper. Cook for another 5 minutes.
In a mixing bowl, combine ricotta cheese, 1 cup mozzarella, and ½ cup Parmesan.
Spread a thin layer of marinara sauce on the bottom of a baking dish. Place a layer of lasagna noodles on top.
Spread a layer of the ricotta mixture over the noodles, followed by a layer of the spinach mixture. Repeat layers, ending with a layer of marinara sauce.
Top with remaining mozzarella and Parmesan cheese.
Cover with aluminum foil and bake for 30 minutes. Remove foil and bake for an additional 15 minutes, until cheese is bubbly and golden.
Let lasagna cool for 10 minutes before serving.