Bring a large pot of salted water to a rolling boil. Add the rotini pasta and cook according to package directions until al dente, typically 8-10 minutes. Before draining, reserve 1/4 cup of the starchy pasta cooking water and set aside.

While the pasta cooks, heat olive oil in a large skillet over medium-high heat. Add the sliced chorizo and cook for 4-5 minutes, stirring occasionally, until the edges are crispy and the sausage releases its vibrant red oils.

Reduce heat to medium and add the minced garlic to the skillet with the chorizo. Sauté for 1-2 minutes until fragrant, being careful not to burn the garlic.

Sprinkle in the smoked paprika and red pepper flakes if using. Stir well to combine and let the spices bloom in the chorizo oil for about 30 seconds.

Add the drained pasta directly to the skillet with the chorizo mixture. Toss everything together, allowing the pasta to absorb the flavorful oils.

Pour in the reserved pasta water, a little at a time, tossing constantly until the pasta is evenly coated and has a silky appearance.

Season with salt and black pepper to taste, keeping in mind that chorizo is already quite salty.

Remove from heat and stir in the fresh chopped parsley. Toss once more to distribute the herbs throughout the dish.

Serve immediately in warmed bowls, topped with grated Parmesan cheese if desired, and enjoy while hot.