Season the bite-sized chicken pieces with salt, black pepper, and Italian seasoning. Pat the chicken dry. Heat a large skillet over medium-high heat with olive oil and butter until melted.

Add the seasoned chicken to the hot skillet in a single layer. Cook for 5 to 7 minutes, until golden brown and cooked through. Remove and set aside.

In the same skillet, add more olive oil and butter. Toss in the diced onion and sauté for about 5 minutes until soft and translucent.

Stir in the minced garlic and sauté for an additional minute until fragrant, being careful not to burn it.

Add sun-dried tomatoes, remaining Italian seasoning, and red pepper flakes to the skillet. Sauté for another 2 minutes to meld the flavors.

Pour in the chicken broth and bring to a simmer, scraping up browned bits from the skillet. Let it simmer for about 3 minutes.

Reduce heat and stir in the heavy cream, letting the sauce simmer for 5 minutes until thickened.

Mix in the grated Parmesan cheese until melted and combined, adjusting seasoning with salt and pepper as needed.

Boil a pot of salted water and cook fettuccine until al dente, reserving a cup of pasta cooking water before draining.

Add the drained fettuccine and sautéed chicken back to the skillet with the sauce, stirring until coated. Add reserved pasta water if the sauce is too thick.

Fold in chopped fresh basil and serve immediately, garnished with extra Parmesan and red pepper flakes if desired.