Soak the cashews in boiling water for 20 minutes, then drain. Blend them with the hot chicken broth, nutritional yeast, dijon, lemon juice, 1 teaspoon cajun seasoning, salt, and pepper for 2 full minutes until glassy smooth.
Toss the shrimp with 2 teaspoons cajun seasoning until evenly coated. Bring a large pot of salted water to a boil for the pasta.
Heat the olive oil in a large skillet over medium high heat and sear the shrimp for 90 seconds per side until pink and just opaque. Move them to a plate immediately so they do not overcook.
Cook the fettuccine until al dente, reserving 1 cup of the starchy pasta water before draining.
Lower the skillet to medium, melt the dairy free butter, and cook the garlic for 45 seconds until fragrant. Pour in the blended cashew sauce and scrape up the spiced bits left from the shrimp.
Simmer the sauce for 3 to 4 minutes until it thickens, then loosen it with pasta water a splash at a time until it pours in a smooth ribbon.
Add the drained fettuccine and toss until every strand is coated, then fold the shrimp back in with any juices. Top with parsley and serve straight from the skillet.