Preheat oven to 375°F (190°C). Lightly grease a 9x13 inch baking dish and line a baking sheet with foil.
Cut lobster tails in half lengthwise. Place cut-side up on the baking sheet, brush with melted butter, and season with Old Bay, garlic powder, salt, and pepper.
Broil at 450°F (232°C) for 8-10 minutes until opaque. Cool, remove meat from shells, chop into chunks, and set aside. Reduce oven to 375°F.
Bring salted water to a boil. Cook cavatappi 2 minutes less than package directions. Drain and set aside without rinsing.
Shred all cheeses and combine in a bowl. Reserve 1/2 cup for topping.
In a heavy-bottomed pan, melt 4 tablespoons butter over medium heat. Sauté onion until translucent, about 3-4 minutes. Add garlic and cook 1 minute more.
Sprinkle in flour and whisk constantly for 2 minutes to make a roux.
Reduce heat to medium-low. Slowly whisk in warmed milk, then heavy cream. Increase heat to medium and whisk until sauce thickens, about 4-5 minutes.
Remove from heat. Stir in Dijon, smoked paprika, nutmeg, Old Bay, salt, and pepper. Add shredded cheeses in three batches, stirring until smooth.
Add drained pasta and two-thirds of the lobster to the cheese sauce. Fold gently to combine.
Pour into prepared baking dish. Scatter remaining lobster over the top, then sprinkle with reserved 1/2 cup shredded cheese.
Mix panko, melted butter, Parmesan, and garlic powder. Sprinkle evenly over the top.
Bake uncovered at 375°F for 25-30 minutes until bubbly and golden. Broil for 1-2 minutes for extra browning if desired.
Rest for 10 minutes before serving. Garnish with fresh parsley.