Cook the Pasta: Bring a large pot of salted water to a boil over high heat. Add the gluten-free fusilli pasta and cook according to package instructions until al dente, about 8 to 10 minutes. Drain and let cool.

Prepare the Spinach: Thaw the frozen chopped spinach thoroughly, then use a mesh strainer to press out excess moisture. Transfer to paper towels to ensure it's well-drained.

Mix the Dressing: In a large mixing bowl, combine sour cream, mayonnaise, garlic powder, onion powder, sea salt, and pepper. Whisk until smooth.

Assemble the Salad: Add cooled fusilli to the bowl with the dressing, followed by drained spinach, dried parsley, and sliced water chestnuts. Gently fold together with a spatula.

Chill and Serve: Refrigerate for at least 30 minutes to allow flavors to meld. Serve chilled.