Add your noodles to salted boiling water and cook until al-dente according to the package directions. Reserve 1/2 cup of the starchy pasta water.
In a large dry skillet over medium heat, toast the pepitas until lightly brown and fragrant, about 3-4 minutes. Add them to the bowl of your food processor.
In the same skillet, add a little olive oil and the diced shallots. Cook until translucent and add them to the bowl of your food processor along with the rest of the pesto ingredients. Blend until smooth, taste, and adjust the salt and/or lime juice as needed.
Season the shrimp with garlic powder, salt, and pepper, and cook in the butter over medium heat for 2-3 minutes on each side until cooked through. Transfer to a covered plate and reduce the heat to medium-low.
Transfer the cooked pasta to the skillet, pour over the pesto, and a little over half of your reserved pasta water. Using tongs, scoop the pasta up and glide it through the sauce until all the noodles are well coated. Add more pasta water as needed. Top with shrimp, toss once more and serve.