Begin by cooking the fettuccine according to package instructions until al dente. Reserve 1/2 cup of pasta water before draining.
In a large skillet, heat the olive oil over medium heat. Add the minced garlic and sauté for about 1 minute until fragrant, being careful not to burn it.
Stir in the pumpkin puree, heavy cream, onion powder, nutmeg, salt, and pepper. Mix well and let the sauce simmer for about 5 minutes, allowing the flavors to meld.
Gradually add the grated Parmesan cheese to the sauce, stirring continuously until melted and creamy. If the sauce is too thick, add reserved pasta water a little at a time until you reach your desired consistency.
Add the cooked pasta to the skillet, tossing it in the creamy sauce until fully coated. Cook for an additional 2-3 minutes to heat through.
Serve immediately, garnished with fresh chopped parsley and a sprinkle of extra Parmesan if desired.