Preheat oven to 450 degrees and spray a casserole dish with non–stick cooking spray.
In a large pot of salted water, cook the spaghetti according to package directions.
In a large Dutch oven, melt 2 tablespoons of the butter and 1 tablespoon olive oil over medium heat. Add the mushrooms, onion, and some black pepper and sautee for 5-6 minutes, or until the mushrooms have softened and the onion is translucent.
Add the garlic, thyme, and red pepper flakes, and saute for 1 more minute.
Add the wine to the sauteed mushrooms and bring the sauce to a boil. Cook for 5-6 minutes, stirring occasionally. Add the shrimp and clams and sautee until the shrimp is pink and cooked through.
Add 2 tablespoons butter and stir until melted, then add the flour and stir until well combined.
Add the cream and half and half to the sauce and stir to combine. Then add the lemon juice and paprika and simmer for about 5-6 minutes, stirring every couple of minutes, until the sauce has thickened.
Add the cooked spaghetti and the Parmesan cheese to the shrimp mixture and toss until the pasta is coated. Transfer to the prepared baking dish.
In a small saucepan, melt 3 tablespoons of butter. Stir the panko and a pinch of salt into the melted butter and then sprinkle the mixture over the top of the seafood tetrazzini.
Bake for about 10 minutes, until the sauce is bubbly, and the topping is golden brown and crispy.
Sprinkle with fresh parsley and thyme.