Prepare your ingredients: peel and devein the shrimp (keep the shells for the broth), finely chop the garlic and parsley, zest the lemon, and chop the pistachios.
Bring a large pot of salted water to a boil. Add pasta and cook according to package directions. Reserve 1 cup of the pasta cooking water for later. Drain and set aside.
Prepare the breadcrumbs: heat the olive oil in a skillet over medium heat. Add breadcrumbs and pistachios, and season with salt and pepper. Toast, stirring frequently, until golden, 2-3 minutes. Transfer to a separate bowl and add the lemon zest, parmesan, and parsley. Toss to combine.
Wipe out the skillet with a paper towel. Add 1 tbsp olive oil to the skillet. Add the shrimp shells and cook for 2-3 minutes, allowing them to caramelize.
Add 1/2 cup of pasta water and bring to a simmer. Cook until reduced to about half, about 3-5 minutes. Pour the stock through a mesh strainer into a measuring cup or heatproof bowl, pressing down on the shells until all the liquid is extracted. Set aside for now.
Season shrimp with salt, pepper, and smoked paprika.
To the same skillet (over medium heat), add 2 tbsp olive oil. Stir in the garlic and red pepper flakes. Cook for 1 minute, or until soft and fragrant, stirring occasionally.
Add shrimp and saute until just cooked through and pink, about 2 minutes on each side.
Turn the heat to medium low, add strained broth back to the skillet, followed by the pasta and shrimp. Toss to coat. Add lemon juice and a splash of reserved cooking water, if needed, to loosen up the sauce.
Top with pistachio breadcrumbs and serve.