Cook the pasta in a large pot of boiling salted water until al dente, following package instructions. Drain and set aside.
Heat a large skillet over medium-high heat. Add olive oil and when shimmering, add the shrimp or chicken pieces. Cook until browned and cooked through, about 3-5 minutes. Remove from skillet and set aside.
In the same skillet, add minced garlic and Cajun seasoning. Sauté until fragrant, about 30 seconds, until you see the spices darken slightly and smell hot and spicy.
Pour in the heavy cream and stir to combine with the spices and garlic. Bring to a gentle simmer, allowing the sauce to thicken slightly, about 3-4 minutes. The mixture should be creamy and coats the back of a spoon.
Return the cooked shrimp or chicken to the skillet. Stir to coat in the sauce and cook for an additional 2 minutes to reheat. Adjust seasoning with salt and pepper as needed.
Add the cooked pasta directly into the skillet. Toss everything together until the pasta is evenly coated with the sauce and heated through, about 1-2 minutes. Finish with chopped green onions for garnish.
