Preheat your oven to 375°F (190°C) and grease a baking dish with olive oil.

Bring a large pot of salted water to a boil and cook the lasagna noodles according to package instructions for 8–10 minutes.

In a large skillet, heat 2 tablespoons of olive oil over medium heat. Sauté chopped onion for 4–5 minutes until soft.

Add minced garlic to the skillet and cook for an additional 1-2 minutes until fragrant.

Add uncooked shrimp to the skillet, flipping them until they turn pink (about 3–4 minutes), then fold in the lump crab meat.

In a medium saucepan, melt 4 tablespoons of butter, whisk in 4 tablespoons of all-purpose flour for 2 minutes.

Gradually pour in 4 cups of whole milk, stirring until thickened, around 5–7 minutes.

Stir in 1 cup of grated Parmesan cheese, adding salt, black pepper, and Old Bay seasoning to taste.

Layer the baking dish with a thin layer of béchamel sauce, then lasagna noodles, half of the seafood mixture, and more sauce.

Repeat layers until all components are used, finishing with mozzarella cheese and dried parsley.

Cover tightly with aluminum foil and bake for 25 minutes, then uncover and bake for an additional 10 minutes.

Allow the lasagna to rest for 10 minutes before serving to help it set.