Bring a large pot of heavily salted water to a boil. Cook pasta according to package directions until al dente. Just before draining, reserve 1 cup of the starchy pasta water.

While pasta cooks, heat olive oil in a large skillet or Dutch oven over medium-high heat. Add the onion and cook until soft, about 5 minutes. Add the minced garlic and red pepper flakes (if using) and cook for 1 minute more until fragrant.

Add the ground turkey to the skillet. Allow it to brown for 3-4 minutes without touching, then use a spoon to break it apart. Continue cooking until no pink remains. Drain excess fat if necessary.

Stir in the tomato paste and Italian seasoning, and cook for 1 minute. Pour in the crushed tomatoes, salt, and pepper. Stir to combine, bring to a simmer, then reduce heat to low. Let the sauce simmer for at least 10 minutes.

Add the drained pasta to the sauce in the skillet. Toss to coat, adding reserved pasta water a few tablespoons at a time until the sauce reaches your desired consistency. Stir in the Parmesan cheese and fresh basil. Serve immediately with extra Parmesan.