Gather and prep all ingredients and set the oven to 375.
Cook the lasagna noodles in salted water until just tender.
In a large skillet, melt 1 Tbsp butter over medium heat.
Sauté onion, celery, and garlic for 5-6 minutes, until softened.
Stir in shrimp, imitation crab, spinach, lemon juice, and Cajun seasoning.
Cook just until the shrimp turn pink and are cooked through.
Remove from heat.
In a small bowl, stir together cottage cheese and parsley. Set aside.
In a medium saucepan, melt 0.25 cup butter over medium heat.
Whisk in flour and cook for 1 minute.
Slowly pour in the milk, whisking constantly.
Bring to a gentle simmer and cook until thickened, about 5-6 minutes.
Stir in Parmesan and Old Bay seasoning.
Grease a 9x13 baking dish.
Spread a thin layer of white sauce on the bottom.
Layer 3 noodles slightly overlapping, half of the seafood filling, dollops of cottage cheese mixture, one-third of the white sauce, and a sprinkle of mozzarella.
Repeat the layers once more.
Finish with the last 3 noodles, the remaining sauce, and the rest of the mozzarella.
Cover tightly with foil and bake for 30 minutes.
Uncover and bake for another 15-20 minutes.
Broil on high for 3-5 minutes, until the cheese is golden.
Let the seafood lasagna rest for 10-15 minutes before slicing.
Garnish with any leftover fresh parsley and enjoy.