Preheat the oven to 375°F (190°C). Cook the lasagna noodles according to package instructions until al dente. Drain and set aside.
In a large skillet, heat olive oil over medium heat. Add diced onion and sauté until translucent, about 3-4 minutes. Add minced garlic and cook for an additional minute.
Add shrimp to the skillet and cook until pink and opaque, about 3-5 minutes. Gently fold in crab meat, and season with salt, pepper, basil, and oregano. Remove from heat.
In a bowl, combine ricotta cheese, egg, and half of the grated Parmesan cheese. Mix well until smooth.
To assemble the lasagna, spread a thin layer of marinara sauce on the bottom of a 9x13 inch baking dish. Place 3 lasagna noodles over the sauce. Spread half of the ricotta mixture over the noodles, followed by half of the seafood mixture, and a third of the mozzarella cheese. Repeat the layers, finishing with the remaining noodles, marinara sauce, mozzarella, and the rest of the Parmesan cheese on top.
Cover the baking dish with aluminum foil and bake for 25 minutes. Remove the foil and bake for an additional 15 minutes, or until the cheese is bubbly and golden.
Let the lasagna cool for 10 minutes before slicing. Garnish with fresh parsley before serving.