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1
Fill a large pot with lightly salted water and bring to a rolling boil over high heat. Once the water is boiling, stir in the shell pasta, and return to a boil. Cook the pasta uncovered, stirring occasionally, until the pasta has cooked through, but is still firm to the bite, about 13 minutes. Drain well in a colander set in the sink.
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2
Heat a large skillet over medium-high heat and stir in the ground beef. Cook and stir until the beef is crumbly, evenly browned, and no longer pink. Drain and discard any excess grease.
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3
Preheat an oven to 350 degrees F (175 degrees C). Spray 2 9x13-inch baking dishes with cooking spray. Combine the 2 cups mozzarella cheese, ricotta cheese, 1/4 cup Parmesan cheese, spinach, and pesto together in a bowl.
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4
Stir half of the cheese-spinach mixture into the cooked beef. Season with garlic powder. Spread about 1 cup spaghetti sauce into a 9x13-inch baking dish. Stuff 12 pasta shells with the beef and cheese mixture, then arrange in the baking dish. Top with the remaining spaghetti sauce, and sprinkle with 1/4 cup mozzarella cheese and 1/4 cup Parmesan cheese.
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5
Mix the remaining spinach-cheese mixture with ham and crab. Stuff the last 12 pasta shells with the ham mixture, and arrange in another 9x13-inch baking dish sprayed with nonstick spray. Pour the alfredo sauce on top, then sprinkle with 1/4 cup mozzarella cheese and 1/4 cup Parmesan cheese.
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6
Bake both casseroles in the preheated oven until the cheese melts and the sauce is bubbly, about 30 minutes.
