Heat olive oil in a large pot over medium heat.
Add chopped onion and garlic, sautéing until fragrant.
Season the diced chicken with salt, pepper, and Italian seasoning, then add it to the pot. Cook until lightly browned.
Pour in the chicken broth and bring to a gentle simmer. Let cook for 10 minutes.
Reduce heat and stir in heavy cream, sun-dried tomatoes, and Parmesan cheese. Simmer for an additional 5 minutes.
Add baby spinach and red pepper flakes (if using), stirring until spinach is wilted.
Remove from heat and garnish with fresh basil before serving.