Fill a large pot with water, add 1 tablespoon of salt, and bring to a rolling boil.
Add 12 ounces of gemelli pasta and cook 8–10 minutes until al dente. Reserve 1 cup of pasta water, then drain the pasta.
Heat 1 tablespoon of olive oil in a large skillet over medium-high heat. Add chicken pieces seasoned with ½ teaspoon salt and ¼ teaspoon black pepper. Cook 5–7 minutes until no longer pink, then transfer chicken to a plate.
Reduce heat to medium. Add 1 tablespoon olive oil to the same skillet. Sauté chopped onion 3–4 minutes until translucent.
Add minced garlic and dried oregano; cook 1 minute until fragrant.
Pour in crushed tomatoes and chicken broth, scraping up browned bits. Bring to a gentle simmer, reduce heat to low, cover, and cook 10 minutes.
Stir in heavy cream, then add fresh spinach in batches, stirring until wilted.
Return cooked chicken to the sauce. Add drained pasta and stir to combine. If sauce is too thick, add reserved pasta water 1 tablespoon at a time until desired consistency.
Serve immediately, garnished with grated Parmesan cheese and fresh basil (optional).